About the number of holes...Get everything set up and measure your humidity. If it's too high add more, if it's too low cover a few up. No big deal.

I believe a lot of people use bungee cord to secure their rubbermaids. I don't have any personal experience with those but that's what I've read. One encircling each end of the tub.

Temperature control is a little harder. I would really suggest a thermostat. This is a good place to get one at a good price .... http://www.mgreptiles.com/index.html ... It's where I got mine. If that's above your means right now then try a dimmer, although you'll have to ask around for more info on that one. A thermostat will keep you from burning your snake! I automatically will shut off and turn back on to adjust the temp. It is a great relief having it. Under the tank heating is great for bps.

As for the aspen and coconut shavings...I believe both are fine! Just no pine or cedar!! BIG NO NOs!

Hope this helps!