Firstly - how big is the viv?
If you're getting a hatchling it may be best to start it off in a small plastic tub (eg. a plastic storage box or a faunarium) so that it feels secure and is more likely to feed confidently. If it's a small viv then you'll probably be ok.
I'd have the mat temp set at around 86F - have the probe directly on the surface of the heat mat so the stat can control it properly. Temps over 90F could be harmful so keep it a bit lower. Cool end temps should be in the 70'sF.
Would also be good (if you haven't already) to have the mat under the newspaper to help prevent any moisture getting to the terminal block.
As long as you have a cool area away from the mat you can leave it on 24/7 as they don't heat the air much at all.
Have one hide over the mat and one well away from it.
You mentioned that one hide was in the middle of the viv - is this because the water bowl takes up too much room?
If you have a bulb of any kind in there the cooler hide really needs to be right at the cool end so would be better to swap places with the water bowl, as long as the water bowl doesn't end up over the heat mat. Also, clear a space in the aspen so that the bowl sits directly on the viv floor - that way he can't get underneath and get squashed. Likewise with any sizeable rocks.
If there is any sort of bulb in the viv make sure that (a) it's got a guard, and (b) it's not powerful enough to overheat the viv. It should be positioned at the same end as the heat mat.
As you're using aspen it would be best to feed outside the viv, in a tub of some kind. If you do feed in the viv put a sheet of newpaper in there and put the food on that, to minimise the chance of any aspen being swallowed.
If it is a hatchling then block the gap where the glass doors overlap with something (if it's that type of viv). It's only a small gap but small snakes can squeeze through so fill the gap with some cardboard or something - but not sticky tape of any kind.
You don't really need to paint the inside of the hides - never heard of that one before. Would be an idea to put them somewhere warm until you get the snake to make sure the paint is totally dry and not giving off any fumes.
That's about all I can think of for now
