Firstly, you can get an EASA PPL when learning on an Annex II aircraft, so ignore that comment from earlier.
Secondly, if you have an EASA PPL with an SEP rating, you can fly a microlight once you have had conversion training. The hours in the microlight don't count towards maintaining your SEP rating which can be a gotcha for some (you will need to renew the SEP rating after 2 years to keep flying microlights) and I don't think count towards getting a commercial licence.
Yes - you should fly regularly to keep up your skills. If you are renting, renters normally put a minimum number of recent hours / flights required before they allow you to take an aircraft. Also you have to fly 3 take off / landings in the last 90 days to take passengers.
The hardest part varies per person. Me - memorising checks...