Thanks a lot everyone. I might go ahead and fill it in steps.
It is a used tank. It's actually an old O'Dell tank and from what I've seen it seems to be a fairly heavily built tank. The glass is about 5/8" thick, I think it's actually 15mm exactly, and the tank is 30" tall. All the silicone looks good but I don't know if it's ever been resealed before. I did successfully test fill it when it was on my garage floor, but of course that was in my garage and it wasn't on the stand. The stand was actually purchased separately and is also used, but looks great.
I guess I just need to man up and do it already. Lol. I will probably wait for the warmer weather that is coming next weekend before getting the hose out.