Hi Riversuir,
Good choice, the basic 2.5amp system can easily be upgraded, but you do need the full 5 amp pack.
I did quite a bit of research on this and all the forums that had posted about it everybody liked it and its proving to be a reliable system.
You can get boosters but you need to split your layout into zones, but the 5amp system will run up to 7 or 8 locos at the same time.
Existing chips are fine with it, as its NMRA compliant.
Not sure about the upgrades though.
Its a very easy to use system and setting up consists is a doddle.
Best of luck with it