Ideally an AFR of 11.5:1 will give the best torque at WOT where 12.5:1 is probably the safest AFR . 10.5:1 might be rich enough for nick's FG. If there's no black smoke present and the power doesn't fall away than it looks good, congrats.
nothing wrong with the 4 speed auto but didn't the MK II have a 6 speed manual. Looks like it was well looked after, the FPV Steering Wheel is a nice touch.
Your engine will warm up faster when the car is being driven rather than when its idling. When its cold , just allow the engine to idle for 30 seconds before driving off to insure that the oil is lubricating the motor. Just drive gently and maybe take a longer route or walk or buy a pushbike.
It's your hi/lo converter , I had the same issue and used the speaker input on my amp or try another hi/lo converter. My 6x9s fitted inbetween the parcel shelf and rear cover, they look to obvious there, may attract some unwanted interest
Headlights on all the time as well. Alot of people don't realise the importance of using your headlights during the day. You will notice the headlights before seeing the car. Why do you think motorbikes have there headlights on all the time, it's a built in feature.