>And I would like to consider return loops so does this feature use up address capacity?
As I understand it, these not inexpensive devices, are attached to the track power and detect the short when the train wheels bridge the gap on entering / leaving the return loop. Once the short is detected, they swap the polarity of the feed in the return loop which removes the short. All this in the blink of an eye, which maybe explains the cost.
>I may have a pool of chips which I can move around depending on which locos I want to have a DCC play with.
After Doug's review on the Hornby Britannia and other people's experience with the Hornby A3, I think your options are limited to:-
1) Permanent chipping these exceptional
2) Not buying them at all
3) Fitting an extension harness that goes back to the tender and having a socket in there which you drop something like the cable free Lenz Silver into - just lift the coal off, and hack out the insides of the tender while you're at it
4) Stick with DC.
5) Build a Z gauge layout in a brief case