I use the Accu-check Combi as well, my second pump had the older blue spirit before hand..
When I'm filling up my cartridge I put in the equal amount of air into the vial as I intend to take out, same as I was taught to do many years ago when vial and syringe was the only option...
So when I'm filling up a full cartridge I inject a full cartridge of air into the vial yes if it's a new vial then there is pressure behind but haven't found this to be a problem though..
As to sets, well I hated the D-links and much prefer the angled tenderlinks which I self insert, the plus side of self insertion you tend not to get the problems of bent cannulars! I've had my 1st bent cannular in 3 years of pumping recently! But it's is preferance at the end of the day, best thing to do is ask Roche for samples try them all and see which one your daughter prefers..
It's the same with insulin in cartridges I have a very small requirement for insulin, so a full cartridge last me around 15 days, which I don't find a problem but will if we're going having a mini-heat wave half fill my cartridge though... When you change the cartridge you don't have to change sets or tubing if it's not your normal day to change, just change the cartridge..
I never found the need to use a 'lifter' or any adhesive remover, no problems with any discomfort removing the patch's, and found that leave very little marks behind, which are normally removed when I have a bath at night with normal washing!