Your assumptions are generally correct, but like all assumptions it doesn't neccessarily mean you've got all the information...
Some Hitec rx's and I believe a few other brands are available in either positive or negative shift. Some of the tx's can broadcast in either shift. Some rx's are auto shift, meaning they will automatically determine the appropriate shift for your tx and Hitec is the one I'm most familiar with being able to do that but I believe there are others. So you just need to be careful that whatever equipment you select will work together.
Then there is the PPM vs. PCM debate/concern. PCM or it's variously named equivalent, is brand specific as most of those protocols are proprietary. So if you want to run PCM which is thought to be superior to PPM for it's ability to reject spurious signal interference, you must run the same brand rx and tx with the appropriate mode selected in the tx.
Do some reading/searching here on the forums and you'll get lots ideas and opinions expressed about various brands/models and their pluses/minuses for any particular application, then you'll have a better idea of what will work best for you.
I don't want to overwelm you, but this is an area where you need to do some homework and it's not nearly as complicated as it might seem once you learn the basics.
Welcome to the forums/hobby and have fun...
