Frequently Asked Questions - Royal Caribbean Shipboard Careers
Will answer most of your questions. Usually any line will expect the employee to foot the bill for all expenses getting to the first ship contract - but sometimes some things can be negotiated (like airfare to the first ship)
Ships that require a MMD (google this or look it up on this forum) will usually pay for that training. Most 'safety' and corporate training happens onboard.
But for any job - you really need to have the qualifications for the job before stepping foot on your first ship, and you just need to look at the job qualifications to see what is expected.