I don't think you have the option to use PCM if using 2.4, so it will have to be PPM, but I'm only familar with FAAST. If your 2.4 is FAAST, you can use FS with PPM, but it has to be set everytime you power up torun, I know its a PIA, but that that way FAAST is setup.

Digitals make noise - just be sure you have it properly centered and setup so there is no straining going on when servo is centered. Digitals make a significant effort to center the servo and if you have it preloaded whne its centered, it will make more noise as its trying to fight back to its centered position. Straining this way can also shorten servo life.

The tx mode for your electic depends on the type rx, you'll need to ID the rx and find out what mode it was made to work in, then set the tx mode to match.

I converted both my 3PK and 3PJS to a 3S (11.1v) last year and they've been fine, just need a prpoer lipo capable charger to take care of it.

I bought my 3PK used as well and I found the manual to be invalueable - manual is located here.