Tank to Sump Plumbing, Return pump, Flow rate

[SeaSerpant]

Hey All,
It's been a while since i've been on this forum! I'm in need of some help. I have a 120g tank that is getting drill and an overflow installed but i am confused about how to plumb it.
I don't know if they are going to put something in the hole so i can plumb it myself or something else.
So to my questions.

How do i make the hole usable for pvc pipes? (the hole is a standard 1.5")
What kind of return pump i need?

I have a bunch of small pumps and i've heard/read that you need 4-6 rotations in your tank per hour. So i would need 480-720 gph. Is this right?
I have 2 Dive power 200's rating at about 200gph. A koralia nano (260gph) and a koralia 1 (400gph) and then i also would have to add the return pump to that.
So thats about 1290gph (of course there is a variation on the actual put out of the pumps).
Is this good enough?

And would i be able to start my tank without a sump by just plugging up the whole by putting the pvc pipe with the "off" switch on it and plumbing it later. But still add rock, sand and water below the overflow with the light and pumps?

Thanks SO Much
SeaSerpant