I can't say much for flow as I don't know what sort of flow those filters would produce. I have a 60 gallon saltwater tank set up but I run two powerheads and a skimmer.
I'd say you'll still need powerheads. There shouldn't be any dead spots and I don't see filters creating all over flow. You want any detritus to remain in the water column ( not settling) so that it can be picked up by whatever filtration you'll be using.
I'd look into a HOB
skimmer over the filters down the road. If you're not setting up a sump. Those sorts of filters aren't the best for saltwater as they can become a nitrate factory if not cleaned often enough. Though a canister might be more useful in a FOWL over reef. Still can't go wrong with a skimmer though.
Someone with more experience would have to speak on flow regarding those filters and such.
I wouldn't worry about the "live" part of the sand. The sand sits on the shelves and in an airtight bag, not going to be much life there. It'd save you money to just go dry.
For rock, I like Macrocks, that's where I got my dry rock. It's very nice, porous rock and their prices are pretty great too.