I'm really pushiong to sneak through before IVA but i haven't got any (decent) alloys yet. I've got a set of rough build alloys though.

I was considering getting a set of R888's and sticking them on my build alloys and then changing them to some decent lightweight alloys when funds allow.

Is it bad for the tyres for them to be re-mounted or is just the once not really an issue? If need be I'll just buy the alloys now but trying to conserve funds for the last minute unseen nasties that I know will probably crop up.

I dont see any problems with what you are planning to do - I've had a lot of second-hand tyres on various tin-top's (and even on my Fury ) with no issues

No, they'll be fine. Ideally you want to make sure that the wheels are the same width aswell as diameter but its not crucial.

As long as proper tyre mounting and dismounting equipment is used it should be fine. However on my Cobra when i replaced the tyres because of age the sidewalls ripped from the beading on all four wheels so I guess it was time to replace them - just as well the tread was hard enough to not generate enough torque to rip the sidewalls when wheel spinning But then the tyres were 20 years old

Personally I'd get a set of 'cheap' tyres of a narrower width for use at SVA on the build rims and get the right wheels and tyres later. That way you could always sell them on later, or keep them back for winter use when the narrower tyre would concentrate the load more and cut into colder/wetter/snow conditions better than a wide tyre.

Tires can be re-mounted w/o any issues. The only risk as mentioned is tearing the bead with the machine. Usually only happens with old tires though.
Cheers.

Yep - if the tyres don't survive the process, then they aren't fit to be used anyway. Expensive way to find out, I know! Between 3 and 5 years is a sensible life for a tyre as UV (sunlight) degrades them..and all tyres for the last 10 years or so have date codes (week/year as a 4 digit code - i.e. 4803 = December 2003)