Are you measuring temps with a digital thermometer with a probe? I feel like you have WAY to many heating sources for your tanks.

You shouldn't need more than one UTH and maybe one lamp per enclosure. More then that is just over kill, unless you live in an igloo or something.

A rheostat and a dimmer are basically the same thing, they basically just "dim" the heat similarly to how you would dim lights. A thermostat regulates the temperature based on the reading it gets from a probe thermometer. You attach the probe to the heat source and set the thermostat to click on when it falls below a certain temperature and click off when it reaches the ideal temperature. A proportional thermostat is one that doesn't click on and off, it just limits the power going to the heat source to lower the temperature. Kind of like a dimmer with a thermometer probe to measure the temp.