jez,
There is a
thread here which covered those sorts of questions pretty well.
Running quickly through your questions though:
1) Yes, the JAR PPL and Class II will cover you. I fly my microlight on that basis. As you say, conversion training is a good plan for any new type.
2) Running costs are low since you can normally do the work yourself instead of paying an engineer and there is no equivalent to the likes of star annuals. You need to renew the Permit to Fly each year for which you'll need to pay an inspector a hundred quid or so and send a small fee to the BMAA. This helps keep one of the contributors here fed, so is in a good cause
Some microlights are administered by the PFA too.
3) The TBO for my microlight's engine is 1,200 hours. I don't know what it is for two-strokes, but I image it is significantly less.
4) If you get something with folding wings that should cut the hangarage costs down, otherwise it's likely to be just the same as any other light aircraft.
5) Hard to say since it depends on you and on what you buy. Landing tailwheel Thrusters supposedly takes some mastering and may take quite a few hours to get the hang of, while tricycle gear types will feel much more familiar to you. My own view is that microlights take more skill to land than the 152s, 172s, PA28s and Cirri that I've flown since the low weight and lack of inertia mean that you are more subject to being blown about and have to pay close attention to energy management. Something light and draggy can stop flying very suddenly from a low approach speed, and if you still happen to be 20 feet up at the time this can spoil your day.
6) If you're looking to spend £5K then clearly the worst depreciation that you can suffer is £5K - not bad in aircraft terms! In fact, once something has dropped to that level it'll probably stay there for years.
7) Just as you say - the running and maintenance costs are less. If you are keen to do night or IMC flying then a microlight is no use to you - horses for courses as ever.