Lucy,
Expect no pay during training. How long does training take? Could be anything, but at least 3-4 weeks. If this is the case, you're very lucky. Lack of line trainers could make it take a lot longer. And you'll be UNPAID while you're waiting.
As far as base is concerned, you can give your preference but the decision lies with Ryanair. Don't expect to get what you want, but for most people it works out OK.
Even though you're rated, you could still be bonded (because of the conversion course!!! What airlines do this?) Demand to see the contract before you agree to this job. Once you're past training, the job's OK but there are better ones out there.
Good luck!