ugf? powerfilter? both?

i am going to be setting up a freshwater 75 or 90 gallon soon. my
questions are basically trying to clear up some indecision on my part
on some basics. there is just as much bad info out there as good i
think so here goes:

1. should i get the 75 or the 90? ive read on some postings that the
surface area will be the same which means the bio load will be the
same. is this true? or will the extra water provided by the 90 gallon
be that much more of a buffer for the fish. right now im leaning
towards the 90 just for the looks. but the 75 will be cheaper.

2. ugf or powerfilter? or both? i have used both in the past but gave
up the ugfs when i owned species which dug down to the plate. i own 1
penguin330, 1 penguin400, and 1 hotmagnum350. i can imagine using all
three on the tank but i continue to hear good things about ugfs.

3. what kind of substrate? ive read that some prefer a larger size
over smaller and vice versa. ive read alot of different theories on
ugf maintenance and the size question has come up more than a few
times, along with exactly how much water you want going through it,
ive read that the more gph the better, and ive also read that too much
can be detrimental.

4. what exactly is the best way to maintain a ugf?

5. one site i visited recommended cutting window screen to size(not
the metal kind) and dividing the substrate into two layers with half
the substrate below the mesh and half above to prevent fish from
digging all the way down and to ensure proper depth of
vacuuming.(?which is?) claims the screen was nontoxic and did not harm
fish physically, and allows for plants to be in tanks with a ugf and
species who will root them up. has anyone else heard of this? might
just be a bunch of bloated syntax.

would appreciate as much info as possible. thanks.