First off, I may have come off a little short/rude this afternoon, so let me apologize. I was not trying to antagonize, I was just having to keep it short and too the point as I had limited time to be on the site, since I was working.
I just have one last post to try and get more info for the OP. If you're not advocating fish in cycling, you're not advocating fishless cycling (otherwise I can't understand why you would not agree with what I am recommending to the OP), the OP's tank is not heavily planted so you're not advocating silent cycling....what is it you are recommending?
I am still failing to clearly grasp the advice you are giving to the OP. If you do indeed believe the OP's tank is ready to stock based off the fact that he has a handful of gravel and deco from an established tank...that is where I'd strongly disagree. IME, it takes more than that to instantly cycle a tank and prepare it for stocking. So, if you would clearly state the advice you are giving to the OP...I'd appreciate it.
Now to answer your question - I'm not advocating fish in cycling, I also am not advocating fishless cycling (in this particular case). For clarity let me say that I agree 100% with the idea of fishless cycling in many cases, and I applaude you for willingness to answer all those questions and help all those people through the process. I'm also not advocating silent cycling (my we've come all long way with all these distinctive terms to clarify slight differences between what are all essentially the same process). What I am advocating in this particular case is too set up a aquarium without cycling at all! Oh I know, I know, just bear with me for a bit . . .
First of all, in this particular case, what we are talking about is an 8 gallon aquarium. The size of the aquarium alone is going to significantly limit our bioload. It is completely within the realm of possibility to set-up any aquarium, of any size, without going through any cycle, introduce fish within a 24 to 48 hour window, and not subject them to any exposure to toxic substances at any time throughout the process. If you know what you are doing.
Second, lets get down to the basics of what we are really talking about here. What is a cycle? The process that we in the hobby define as "cycling" is a process that we follow in order to introduce and build bacteria levels within the aquarium to a point that they can be in balance with the biological waste load that is produced by the fish and other living organisms that we introduce into the aquarium. Agree? Further, our goal is to establish two to three different populations of bacteria within the system, those that convert fish waste into ammonia, those that convert ammonia into nitrites, and in some cases (usually in saltwater aquariums) those that convert nitrites into nitrogen gas.
The key word here is balance.
Now, where are those bacteria going to be found living in our aquarium? The answer to that question is not as cut and dry, nor as simple as many try to make it. The simple truth is that these two or three populations of bacteria are going to become established throughout the aquarium, and where they establish (at least in part) and to what degree is going to be determined by a lot of different factors; things like water flow rates and turn over rates, type/method of filtering, choices of substrate (bare bottom, sand, gravel, peatmoss/sand mix, etc), and other hardscape features such as rocks, plants (real or fake), and aquarium decorations. The majority of beneficial bacteria may or may not be found in the filter - depending on the type of filter being used, the filter media that is contained with the filter, and all of the factors that are mentioned above. If your filter has a high enough turnover rate, that it can effectively pull every bit of biological material introduced into the system (either food or waste) in or through the filter prior to it touching the bottom substrate, that may in fact be true.
Given however that in most aquariums this is not the case, than invariably some of the waste/food is eventually going to settle onto the substrate and other hardscape features, and we have to accept that bacteria colonies are also going to establish within those areas as well. To what degree they will colonize those surface areas will, as stated, depend upon the factors described above as well as some others I haven't mentioned.
Remember that what we are looking for here is a balance of bacteria to waste material/left over food. If in fact, we introduce a substantial population of bacteria and decomposing organic waste into a new set-up aquarium, the populations can be balanced within the tank within a very short period of time. The key is getting a substantial enough populations of the desirable bacteria and enough organic material to fuel their growth.
This can easily be accomplished through the transfer of water and substrate from a mature aquarium. The key is in the volume of substrate and the quality of water that is being transfered. We do not want "normal" aquarium water for this purpose. As you said, the amount of bacteria present in normal aquarium water is minimal, however it is certainly no where close to being sterile - try placing clean aquarium water onto an agar plate sometime and see how many 100 to 1000s of bacteria colonies will grow from that contact. Regardless, what we want for this process is the nastiest, dirtiest, grossest water we can vaccum up out of our bottom substrate - gravel works very well for this, as will sand or peatmoss/sand mixes - bare-bottom tanks will not. Why? Because that gross, nasty, dirty water is going to be absolutely loaded with the desired bacteria and decomposing waste that we are looking for. In this sense, the process is similar to what you are trying to accomplish when you do your fishless cycle by introducing ammonia into the system in order to build the bacteria levels. The difference is in the introduction of an already existent population of bacteria.
In the OP's situation, he already has a gravel bottom, and a very small tank, making it very easy to transfer the desired amount of bacteria/waste required to stabilize this tank from the very beginning and avoid the "cycle" all together.
You mix the material gravel in with the new (in his case, he would need to drain as much water from the tank as possible first), then you pour that nasty disgusting water in till it just covers your substrate. Then refill the aquarium with new/clean water. Allow 24 hours for settling and heat stabilization, and begin the testing process. Once ammonia and nitrite levels are in the safe zone, you begin
slowly adding fish. So long as you add the fish as soon as those levels drop, you are introducing a source of waste and bacteria levels will not die off. So long as you add fish slowly and in reasonable ammounts, don't overload the system too quickly and don't overfeed, bacteria levels will grow to accomidate the bioload, and you will not suffer ammonia or nitrite spikes of any type. You will need to monitor chemical levels daily in order to insure that you are not over feeding and that you are not introducing too large of a bioload, but this is no different than what any of us do (or should do) any time we introduce new fish into any aquarium.
Again, the process here is no different than that of setting up a saltwater tank using already cured LR - you are introducing the desired bacteria levels from the beginning rather than slowly growing them.
You do this even with a cycled tank. If I follow the method you describe and fully cycle my tank, then introduce only a single fish into a large tank for a period of a month or so, what will happen to my bacteria levels? They drop right? Then I go out and buy several more fish and introduce them into my tank (say 3 or 4 smaller ones). Are the bacteria levels in the tank going to support the addition of those fish without a cycle? It will, but the bacteria levels will have to increase in order to do so - does that mean I've exposed those fish to toxic levels of chemicals? Not if I did my job right and reduced feeding and monitored chemical levels to ensure they do not rise to toxic levels. Might I have to do some water changes? I might, but if I introduced a small enough addition to the bioload and give the bacteria levels time to rise in response before I increase it again significantly I most likely will not need to.
Does that help to clarify my position?