There really isn't much difference in using the magic trackpad then the trackpad built in to the MBP at least those with the force touch if you have one.
I have the mid 2015 with force touch. When pairing the magic trackpad, the trackpad settings will not change to those of the magic trackpad like in previous MBPs. It will still show the force trackpad settings. I always liked using the three finger drag and you have to set that by going to accessibility/trackpad.
I always use a separate trackpad, mouse, and keyboard for my MBP because I need to raise my computer to a comfortable viewing level. This setup serves my needs perfectly since I decided to replace my iMac with the MBP.
I use my Magic Trackpad with the 13" rMBP when it is on the TwelveSouth Hi-Rise stand.....use a Magic Mouse and the trackpad with it, along with the Apple wireless keyboard. Works out very well for me. When I'm off somewhere away from home with the rMBP, no problem, I just use the actual trackpad on it, then.