I like it. Looking good.
Next step: drill bulkheads and silicone in the acrylic. I have a diamond hole saw on the way but I'm still really nervous about drilling into my new, expensive tank. It's currently in the 30s (F) outside, and I'm not sure if the freezing air + freezing water will be an issue for drilling.
I would also worry about drilling glass in temps that cold. Glass is brittle enough at room temperature. Maybe others have more experience with this. You could do it inside, though. I do all of mine inside. You don't have to use a hose to run water over the bit the whole time. You can use a little dam of plumber's putty and put the water (or antifreeze - that's what I use, just try to keep it as confined as possible and wash anything it touches thoroughly before use) in it.
If it's nice out, do it outside. But you aren't describing "nice out". So do it inside.
Uh - are you sure that's an acrylic tank? And, does one even use diamond-coated tools on acrylic? A steel hole saw for wood all I've ever used. Honestly I like drilling glass way
more than plastic - melty stinky plastic is a pain in the ass, I fucking hate it. You really have to manage heat build-up, it's so much worse than glass. Arrghhhh. Anyway...everything below is based on diamond & glass.
The putty dam technique works great
. Alternatively, get a helper and a squirt bottle and have her/him pumping a constant spray of water onto the cutting surface. It doesn't take a whole lot of water. Just go light and slow with the drill - don't bear down at all, and don't go full-speed.
With a putty dam I usually set up the tank on something elevated - saw horses, a pair of tall buckets, whatever, as long as it doesn't wobble - and under the tank I lay a towel and then put a small bucket on that. Under the hole-to-be. Hang on though - I'm talking as if you're doing a small viv or a big lid (a flat sheet). With your bigger viv, if you can find a catch-container that'll fit completely inside the viv, you can just lay down your towel on the floor, put the catch-container on the towel, and lower the upside-down viv over the container. Drill the tank bottom from the outside. This will be better, ergonomically speaking - just kneel beside, or stand and straddle the tank, and let gravity do all the drill-pushing. You just hold it up. It can get a little tiring drilling thick glass, slowly.
With a spray bottle, you can just put the tank on several layers of spread-out newspaper. That's enough to catch the little bit of water that you're using. Nice thing about the spray bottle (or hose, if outside) method is, you can do it vertically. No need to flip the tank and deal with the open doors if you're drilling the back.
Your biggish tank is gonna have thicker glass, which takes much longer to bore through, so I'd take more care with cooling. In this case, for a newb without a hose running the whole duration, I recommend the putty dam. Modeler's clay is what I use. It's what was laying around. I just keep a ball in a ziplock, and when I need to use it again, I put a little water in and let it sit overnight. Then I knead up a "hot dog" and make a ring about 4" across.
Either way, when you've gotten the center cut out, take a little care getting out the glass dust. A few wipes with a damp paper towel is good enough.
I've drilled a number of vivs and lids, with zero breaks. And now, my wife is getting into stained glass, and she's got me cutting colored glass circles (what we throw away - I find that amusing) which she uses in her art. Still, zero breaks. Cutting holes in glass is easy
with diamond hole saws.
Good luck! You can do it. Just don't push, and don't be in a hurry.