What do I need to order for plumbing on a 20 tall

[samdaman]

My list so far:

3/4” ABS Bulkhead Slip X Thread (Slip on the Flange/Head side)
$4.99 $4.99

35mm Diamond Coated Glass Drill Bit
$10.49 $10.49

CPR Aquarium Return Jet for use with 1/2" and 3/4" Hoses
$7.75 $7.75

3/4" Schedule 80 Elbow Slip x Slip (2)
$1.75 $1.75

3/4” Schedule 80 Coupler Slip x Slip

what else do I need, this is my first time so bear with me!

[coralnut99]

The list will vary greatly from settup to settup, so just asking what plumbing supplies you need is just a bit vague. You should describe a bit more of what you're trying to accomplish so others can chime in with thoughts. The one thing I'll throw out there is that Schedule 80 is WAY overkill for anything you're trying to accomplish. Plain old Shedule 40 is very much the standard for 99.9% of DIY plumbing applications in the hobby, and you'll find it infinitely easier and cheaper to buy.
A general word of advice would be to keep extra fittings and pipe on hand. The few extra bucks will save you many hours in trips back and forth to the store.
A specific word of advice would be to give lots of thought to how you arrange your plumbing, and support fittings and plumbing runs properly. The glass on any shape 20G is on the thin side, so the weight of a fitting attached to a length of pipe can stress the glass panel and crack it easier than you think, even if you snug up the bulkheads properly.
HTH