Your questions are related. You need to get the t-visor that best fits your helmet. For instance, I had an FPH2 helmet, so I used the FP Deluxe visor. The descriptions indicate which helmet the visor fits best. Note that after installing, I still had to trim the visor a bit... actually I sanded it down, but it still needed some fitting.
As to whether or not you could repaint a ROTJ helmet to an ESB helmet... well, the damage is not the same on both helmets and there are some minor differences between the helmets. Personally, given all of the work that goes into painting a helmet, I would get the proper one. I am not as detail oriented as most, but painting a helmet is hard work and you are going to want to get it right. As you lay the layers down, you start to see how the damage fits with the paint job.
