Don't use a 6" hole saw. Use a reciprocating saw, skilsaw and cut out the hole.
And again, you should use the 12gal HDX totes. You're not gonna be buying each piece of 2" abs in pre cut lengths I hope either. Just buy a standard 8-10' piece and cut it down as you need.
Also I'm not sure we your 2" elbows are female to male. Just use female(slip) on both sides and glue it. Don't think of bends as needing threads. Just buy new ones if you ever were to change anything. Just make where bulkheads meet pipe, threaded.
Also why does it say you need 4 2" elbows?