1.CP makes the Cheeta/Cub line , I cant think of who makes the Trex off the top of my head.
2. It all depends on if you have cut your plastics, but any mounts not being used. the small tabs by the front of your motor and pipes.. theres metal all over you can cut off. Just have to make sure its not holding anything or reinfocing anything.
3. I'm not a RZ/RD guy so I dont have alot of experiance with them, but yes they will fit banshee jugs
4. The length of swinger is realitive to your motor build your weight paddles all kind of thing... Most common would be a +4 but keep in mind you want to limit your jumping with an extended swinger.
5. Cant help with the spindle issue never run a j arm, send Dajogejr a message he would know he runs a j arm.
Just make sure you do your suspension in relation to your motor... if you spend a ton on going fast but no suspension your not going to do much but spin your tires or watch the sky... start researching the info... its been covered TONS of time on here. there is alot of reading to be done on your part. Dont go and stat buying shit until you understand whats needed and not needed.