bigger the better... my one male is outside 24/7 in a 4x8 and he cruises the whole thing. Make sure the sides are taller then he is long, they climb very well and will escape!
I see that you live in Arizona. The aquarium you have set up for your Russian tortoise is ok for night time, however the tortoise's main, daytime habitat should be outside. That Russian is big enough to be an outside tortoise.
About your aquarium:
Its not big enough
The waterer isn't good for tortoises (a plant saucer is better)
It looks very pretty and comfy for the tortoise, but just not as the main home.
If you don't have enough room outside, then you're tank will have to do and I think if you have the proper temps and enough UV for the little guy, your tank will be just fine (i think the size will work for just the one tort, but I'm no expert either) I do agree that your water bowl should be swapped out for something shorter. Looks pretty good to me.
Even if he can't live outside, at least you can take him out frequently for some exercise and sun