the contribution per year is now £3600. You can move to another provider and the total you transfer will not count towards your 3600.
eg if you have put 2000 in your current iSA this year and the total in there is now 5000 you can move the whole 5k and then add a further 1600 so you have still only deposited 3600 of new money this year. A lot of providers are giving better than 4.5 but some are no withdrawels allowed, or you can but loose a lot of interest so check the sall pring not just the interest rates.Answer 2
I think the maximum is one ISA and £3000 per tax year, so you couldn't start another ISA, unless you haven't paid anything into it this year, but there may be another savings option with a higher interest rateAnswer 3
Dinner Nanny's answer is a goo one AND it's correct