Praslin 3 days

Need suggestion

Travelling from mahe to praslin on 25 aug

1.shall I book ferry in advance or just booking at counter will be ok

2.how much should taxi cost from ferry arrival point to hotel castello.

3.how should I plan 3 days in praslin. I am only used to driving in plains with less traffic not sure about praslin roads. So not able to decide on car rental or travel by bus.