Let me be the first to welcome you to Pinside then! I am a newbie too, only about 4 months under my belt, so I can't offer a lot of deep advice.

Two that I can address are #4 and #5.

#4 You think it is connector, not coil. You can confirm this by turning off the machine while the flipper is in the stuck position. If it is electrical it will instantly drop back, mechanical it will stay there. Most of the time mechanicals are related to the plunger getting hung up inside of the coil. New coil sleeve will most likely take care of the problem, but while you are at it take a look at the coil stop (goes in the other end of the coil.. the plunger rod hits it when you activate the coil and it sucks in the plunger) sometimes these get distorted. Also while you are at it you can replace some or all of the flipper assembly. At least here in the States these are relatively inexpensive and easy to get.

#5 There is a HUGE discussion on this, (do a search when you have a lot of time on your hands). My opinion is to use some 91% or greater rubbing alcohol for a general deep clean, if you have serious dirt/wear/swirl marks a Mr. Clean MagicEraser does a fantastic job - use that alcohol again instead of plain water (just go easy so you don't eat right through the playfield). Follow this with some Novus 2 to give it a final gentle abrasive, then hit it with two coats of automotive quality hard carnuba wax (in a can- not a bottle).

As I said, these are my opinions (your mileage may vary). If anyone disagrees, I am always open to other suggestions myself.

In any case... congratulations for finding pinball again and for finding pinside!
Chris