Hi Ant - your best bet will be to go to the RSOC forum & register there, then go to the FRS section as you will get answers from the owners pretty quickly as tbh for FRS owners Passionford is dead quiet tbh - there are loads of helpful & knowledgeable owners there who can help you out

http://bbs.rsownersclub.co.uk/forumdisplay.php?f=134

To answer a couple of your questions the dried coolant on the thermostat housing indicates either a housing that is leaking slightly or has leaked in the past & been fixed with a new gasket but not cleaned up

Re the dump valve, yes you need one & ideally it should be a recirculating one as fitted to the car as standard - atmos ones can cause the FRS to overfuel & not run correctly - basically the FRS is not designed to run without a dump valve due to the spec of the turbo fitted to our FRS

Out of interest seems like you've bought one with a bit of work done to it then based on the front mount intercooler setup thats fitted to it