Welcome aboard, Sam.
Many of the faults you list are common. The fuel flap release problem could be the switch, the relay or the mechanism. Press the button and listen for the relay click. If it clicks, then the switch is working and the problem is either the relay sticking or a mechanism (linkage) problem. If the relay doesn't click then the fault is either the switch or the relay. Replacing the relay is VERY fiddly, much more so than replacing the switch.
The manual release procedure for the filler flap is to remove the driver side boot panel and pull the linkage downwards to release the peg on the filler flap. In my case the relay had stuck in the open position and some clown had bodged the spring mechanism holding the flap in place so that you could open the flap with a finger nail or credit card!
Engine misfire could be one of a hundred things so, as previously mentioned above, invest in some diagnostic capability. Most here use VCDS, I use OBDeleven Pro. Horses for courses.
A word to the wise. I would urge you to take the 12 months MoT with a pinch of salt and physically examine for yourself cv boots, drop links, track rod ends, brakes and brake lines for piece of mind. It never ceases to amaze me how 20 year old cars magically manage to sail through a pre-sale MoT when they are misfiring, showing visible signs of neglect and generally clearly being worse for wear.
I have spent £4k in the last 12 months dealing with overdue maintenance issues and remedial repair of various oil leaks, as well as badly worn suspension and brake components. But the car sailed through it's pre-sale MoT! It really doesn't mean anything.
We all love our A2s here but don't for one moment think it is cheap motoring. Many of these poor little things have suffered the most horrendous abuse and neglect. Mine certainly did. Think of this club as some sort of donkey sanctuary and you won't be far from the truth!
Good luck and welcome to our eccentric little tribe.