I agree that bulkhead and cap could've worked well. But honestly I did not drill the hole well at all - it was pretty messy if you looked at it from the outside, and there was a very tiny crack near the surface coming from the hole. So putting a bulkhead on it would have increased stress on the glass and could have cracked.
Also, when I put in the bulkhead on the new hole, I was dumb enough to paint the back first and then put the bulkhead, so it didn't make a good seal and it leaked! So I'm even more glad that the leak was in a hole up above so not as much water leaked onto the floor.
As for draining the tank from the lower hole for water changes - the tank is about 3" from the wall, so I could not really drain the tank from the back. That could've worked if I had drilled the side.
All in all, I'm really happy with how it turned out and my fish and livestock seem happy so far, too!
