MCS is what's called an IDE, an Integrated Development Environment or put another way, a glorified text editor. You don't have to use it, you can write your programs in any text editor. I do recommend using MCS, I just want make it clear that it's not NEEDED.

PBP is the compiler. The compiler converts your program into assembly language but that's not what the target device is using so in comes the last part, the assembler.

The assembler takes the assembly code and converts into a binary file ready to be loaded into the chip your targeting.

Previously, PBP used to ship with it own assembler, called PM, but it doesn't any more. In fact, the newer versions of PBP requires the use of MPASM or MPASMX. The checkbox in MCS is (or was) used to select if the compiler, when it's done spitting out assembly language, should invoke PM or MPASM. Since PM is no longer supported you should invoke MPASM(X) and for that to work you must have it installed - it comes with the MPLAB(X) IDE but I think we've covered that before.

I don't have time to look up the datasheet for your part right now but you are correct that you can not and should assume that just because you did it one way on one chip it's the same for the other chip.

/Henrik.