For you, Demon Tweeks (Wrexham, all though I have never been there myself so am not speaking from experience) and get them to fit the lot or source the various parts on the interweb and then get a specialised place (such as Demon Tweeks etc) to fit.
Do a search on here re Maps, Zorst and other bits and loads of stuff on everything you need to know d will give you a few ideas on different manufactures you may not have considered.
http://www.mk5golfgti.co.uk/forum/index.php/board,33.0.htmlMaps, the big boys are Revo, APR, Bluefin and some great indies, many of them are forum members.
WHOLE section on here just about tuning.
Milltek are great systems, also have a look at Blueflame, Scorpion, APR, BCS and jetex.
Dump valve (the Diverter Valve, Revision D is the latest version, piston type) and can be bought anywhere inc. Stealers for about £50.
Oh and welcome to the forum! Get some pics of your new purchase up ASAP!!!!