You can start with the crushed coral...it'll just be a pain to remove and then add sand. This stuff really won't do anything in terms of getting your tank cycled, you need an ammonia source for that. This bagged sand and such being marketed as 'live' is false advertising IMO
, but I'm not going to put the stuff under a microscope to see if there is any bacteria in the water...I wouldn't know what I was looking at anyway.
A good rule of thumb for any pump is to put a ball valve on the return end of the pump so you can adjust it to where the flow through is perfect.
In terms of a skimmer, you might not need one on a FOWLR
system and an ATS running on it. You'll get an idea of how things are going as the system gets up and running in terms of what your parameters run at and what needs adjusted. You totally can add one, but why if you don't need to?