Hi!
You've got some great questions and I'll try my best to answer them.

The first thing I noticed was that your warm side temps are pretty low for a ball python. Many owners keep the warm side from 91-94F and the cool side at about 82F with ambient (air) temps at around 80F.

It sounds like you have quite a depth of substrate in your snake's cage and this depth might interfere with the flex watt doing its job. Could you perhaps decrease the amount of substrate?

You mention that you have a light on all the time to help with heat. If this is a white light bulb, your snake is not appreciating this methodology!! They really need a distinct 12 hour daylight and 12 hour darkness cycle.

Rheostats are inexpensive and are also a real pain if your room temps are not really constant. Any fluctuation in room temps of more than a degree or two will mean that you'll be constantly adjusting the rheostat.

I would recommend for your situation purchasing a thermostat and flexwatt and decreasing the amount of substrate. With this approach, the t'stat will monitor the heat output for you and the flex watt will be able to do it job. If you discover that the tank is still too chilly, or the ambient temps are too low, you could wrap the sides and back of the tank with insulation.

A terrific place to purchase flex watt and t'stats is Reptile Basics (http://www.reptilebasics.com/Heating-p-1-c-248.html). You could also email Rich (the owner and an extraordinary person) and ask him what might be best for your situation.

As for the ladder, I'd take care to not hang it too high. While some balls tend to be climbers, they are not arboreal; meaning they fall! Perhaps you could affix it from the ground to the side of the tank?? This type of jungle gym might be safer for him in the short and long run!

I hope I've addressed your various concerns and questions! Take care.