Ok. First of all, new xboxes (slim) don't rrod at all. Initial versions of xboxes had the quality issues, but even recent regular version of non slim had that problem eliminated.

If you want to extend your hdd for xbox, just buy regular 2,5 hdd and install it. It is easy, youtube has bunch of tutorials.

Welcome aboard, and feel free to ask more questions.

 

1) RROD is caused by the system GPU and CPU heating up way more then they should
over time the constant heating and cooling causes cracks in the solder bridges under the chips (mainly it was the GPU), there was only 1 temperature sensor and it was located on the CPU and the GPU got way hotter then the CPU but would never trigger the sensor
the 360 slim now has a combined GPU and CPU chip which has a 45nm fabrication
this allows it to use less energy and produce less heat
it is possible that RROD can still occur but its very unlikely, a fan isnt really needed now

2) yes, you can slip in an authorized 360 hard drive into the 360 4GB slim, if you want to use third party hard drives, it only works with a few of them
http://digiex.net/guides-reviews/console-g...x-360-slim.html

3) regular xbox 1 controllers will not work with any version of the 360