The Zoo-Med Repti Temp controller can be found online a lot cheaper. I would recommend a 150 watt emitter. They are only a couple bucks more and for a heater it is better to be hotter than not hot enough. I have a Zoo-Med 150 watt emitter on an ESU controller. ESU changed their name to Zilla I think so I got it cheaper. Look around at reptile supply places on the web and you should be able to find a controller for around 30 bucks.
No a rheostat is like a dimmer on a light bulb. A controller works as a thermostat where you can set the temp and it will turn the heat on and off to keep the area at that temperature. Reptile supply is where I purchased a Zilla (formerly ESU) controller.
They have two from Zilla one will handle 500 watts and the second handles up to 1000 watts. Here is the link to the 500 Watt model. http://www.reptilesupply.com/product.php?products_id=2534
Mine is the Repti Temp 500R like the one you posted. I suggest you choose an emitter size based on the size of your cage. A large cage would probably be ok with a 150. The cages I use are various sizes with the largest being 40" x 20" x 20" high.
Well I am going to use a 3 x 2 or 2.5 cage made out of PCV plastic. I am not going to clip the heater on it, so none of the heater will be touching the cage. I Am also going to make a lot of venalation. What do you recommend?
I suggest building the cage, then get whichever brand of thermostat you are going to use as well as the fixture and then when everything is done buy a 100 watt and try it to see where you have to set the dial. If you have to have it set way up high to keep it warm enough, then go to the 150. If you barely have to move the dial, then you might get away with a 60. I would definitely have the cage done before buying.
I have a huge cage so I use the 150 watt emitter. I have actually thought about adding another 150 watt but then it might be too warm. My cage is a Marchioro Tommy 120 which is 2 x 4 x 22" I think. Both types of controller are good ones. I have heard good things about both. I just got the Zilla one cuz it was cheaper at the time.
Another thing to consider when getting an emitter is the temperature of your house. If you keep it at 68F the emitter will need to provide much more heat than someone who keeps their house at 72F. The ReptiTemp 500R has a dial that you rotate to reach the desired temperature. It doesn't have actual degrees. Ideally, the dial should be about half way as that will give you the most adjustment, either up or down.
The problem I have with the 150 for my application is that I have to have the dial just about to the lowest it will go which doesn't give me any adjustment to go lower.