I follow the slimdevices.com forums fairly closely and don't recall seeing any unusual volume of problems with SBS 7.4 or 7.5 and Transporter.
Keep in mind that with as diverse a population of servers (Windows, Apple, & various Linux incarnations) there are always going to be a few that challenge any upgrade. Also note that a forum such as the slimdevices one is going to draw out those with problems. People who had a problem-free upgrade often don't take the time to post that everything went fine.

You will need to run version 7.5 with your Touch. While I don;t have a Transporter, I found 7.5 runs perfectly fine with my SB3, Duet and Radio as well as the new Touch which has been up and going for 10 days now.
Also keep in mind that all of the old versions are still available for download if you feel you must retreat to an earlier version.