1. yes, get it fixed, for the cost, do both sides and change the entire control arm not just the ball joints. Think I paid 40 quid a side last time.
A garage will charge you for their time, pulling the control arm off to get it in a press is going to take longer than just swapping it out. so it often works out similar in price to change the whole unit. This also gets you new inner bushings at the same time, a little bit of preventative maintenance. other things to have looked at while the garage is in there are antiroll bar drop links and tie rod ends, but these aren't needed unless they are showing wear.
2. Technically it's an advisory at the inspectors digression, intended for when they look like the lack of coating may lead to failure. some inspectors (mostly new to it) are more willing to give the advisory when it isn't needed. Not saying it's a way for the garage to get more work from you, but I've known a few who do this. don't worry about it, it's only a fail when a spring snaps and is no longer secure in the seat.
3. Quit likely a corroded disc or a sticking piston on the day that's settled out. if the car doesn't pull one way or the other under braking, don't worry about it, but do keep an eye on your pads and discs.
