if you flash a stage 1 map on a stock engine, you should see gains of around 60bhp (thats where mine is). however, I would recommend an induction kit / air filter and an uprated exhaust system before mapping the ECU. you can see gains of close to 300bhp, however be mindful of the knock on affects on the clutch. I have heard reports of the stock clutch slipping at 300+ bhp.
1. Halfords sell genuine VW touch up kits. I personally wouldn't use one, I'd be tempted to speak to a firm such as 'chips away' and have a decent job done.
2. all GTi MFSW have the bluetooth buttons, but not every car has the upgrade option. there are a few companies around who retrofit such things. I'm in the same boat as yourself, however it's never really bothered me.
3. there is a detailing section on the forum, however for tornado red I would recommend Auto Finesse Spirit wax with 3M Ultrafina polish.
4. here's a link to my build thread:
http://forum.un-phased.co.uk/index.php?topic=7521.0 - it will give you an idea of what mods can be done.
5. I believe the 2011 generation build GTi's aren't affect by the tensioner issue, however it would be worthwile to check the info thread on exact dates of the revised parts.