Should you proceed with training for an FAA license in the USA, upon passing your final checkride with the examiner you can fly that same day with the “Temporary Airman Certificate” you will be given on the day (your plastic card will come in the post subsequently). Back in the UK, it is possible that you can self-fly hire helicopters on your FAA ticket, but will be at the discretion of the location (back in 2006, I did SFH on my FAA for 3 months until receiving my JAA). Your FAA license will be valid for life and only require a Biennial Flight Review and valid FAA Class III Medical to remain valid and does not have type ratings for helicopters under 12,500 lbs.
As for conversion to EASA, the term is incorrect as you are actually getting another separate license. You will have done most of the requirements under your FAA training, but will need to do the following to sit your EASA examination checkride:
- 9 written exams & radio verbal exam (FAA has just one big computer-based exam)
- 5 hours instrument awareness dual flying (flying with the “foggles”) unless this requirement has changed; it was the main difference in FAA and European Syllabi
Regarding training locations, Cloud 9 noted above is in West Palm Beach as is Ocean Helicopters (both good, but over an hour drive from Miami). I would also look at The Heli Team in Orlando – also owned by a Brit.