First, Welcome to KiteLife! We are glad you are here.
There is a bit more pull to the 2.5 but these are both sport sized and you can pull a buggy with either. The difference in pull between the 2.2 and the 2.5 isn't major but it is noticeable. I've said it often that the 2.2 is the sweet spot for the quad conversion but I have done a 2.5 for Chris Shultz at HQ Kites. At one point they were considering making it 4 line capable due to that work.
So to bottom line your answers.
Yes there's a difference in the sizes but all things considered it's not a HUGE difference.
Yes, Both of these sizes are good candidates for 4 line conversion.