That dream sounds a lot better than the first one! I'd opt for a 20 long sump though (that's what I did), which you can pick up for $20 at petco next time they have their sale.
If you haven't seen it yet, check out my build thread. I think I asked just about every question possible (even before that, which is linked in my build thread where I did some initial planning). Finally - 40 Breeder Reef Journal/Build Thread
I really like my 40 breeder, and a 40 tall is about the same, only slightly narrower and a bit taller IIRC. Still plenty of options and would definitely get you started.
Here's what I'd look in to getting-
50lbs base rock - $85 from reefrocks.net
40lbs sand - It was $15 shipped from reefrocks.net with purchase of rock... not sure if that's still going on
Heater - $20-30?
Refractometer (measures salinity... much better than hydrometer) - $30
Powerheads - This can be as cheap or expensive as you like. Two koralia 750's (about $30 each?) will get you about where you need to be... or you could go with an MP10 (my favorite), and you can find those used online for $150+ used, or about $250 new.
If you're going to do a sump, I'd highly suggest drilling. For $79 (I think), you can get a 750gph overflow from glass-holes.com (make sure you put the dash... trust me). A much better method than an HOB
overflow, and very simple to install. Add another $10-15 for plumbing parts, a good return pump (mag 7 is what I went with... another $80 or so), a skimmer (get in on a BRS group buy and get a bubble magus NAC 3 for about $120)... I think that about covers you. An RO
unit will save you some money though. BRS has a good 75gpd unit for just over $100 and then salt is about $50 a bucket and will last you quite a while (the initial bucket will go faster since you're making more water to fill it up).
As far as fish are concerned, you've got a ton more options than you would with a 10. There are a lot of fish you can put in a 40g, just make sure to do the research like you do in FW
in terms of compatibility and tank size requirements.