I am debating on buying a big reptarium to ensure he gets to be a decent size, but have been hearing conflicting information about them.
The size of the enclosure has no bearing on the future size of your BP, however large enclosure can be overwhelming and stress your BP.

Also if you are thinking about the apogee reptirarium those are not meant for BP but for lizard, they do not allow you to maintain proper temps or humidity needed for a BP as they are made of nylon type screen material.

I would also recommend 2 tight identical hides (with all sides touching your BP's body)

As far as thermometer/hygrometer the dial device that I see in your enclosure are not accurate and I would recommend you to get a digital Thermometer/hygrometer (something like this will work just fine )

Well the temp is always 80-87 varying throughout the day and night
Temps should remain constant day an night, offering a gradient of 80-84 on the cool side and 90-94 on the warm side.

Also what I did not see in your list

Do you have a UTH to provide belly heat? Do you have a thermostat to regulate the temps and avoid over-heating?

I would also recommend you to go over those

http://www.ball-pythons.net/modules....warticle&id=59

http://www.ball-pythons.net/forums/s...004#post569004