You are looking for THE BEST GUN THAT WILL NEVER BREAK!
Internals are important of the AEG, Don't worry on the externals yet, Focus on the part that it makes it run, A Ris won't let your gun run it is the mechbox...
If you still want a good running gun search around for a good gundoc if you aren't experienced doing internal work, Buying a gun will be good but having 2 will be great.
If you don't want your ICS anymore leave it in your closet and get a WE m4 they have less problems than the king arms in my experience.
Make your choice and do it, you got money well go spend it...