You will be allocated SVFR, no need to specifically file IFR unless you choose to.
Guernesy ATC is one of the most friendly & helpful ATC's I've ever come accross.
The Fermain Hotel has lovely views and is in St Peters Port, about a 10 minute taxi ride from the airport.
The Channel Islands are well known for sea fog especially in Summer months which can occasionally linger for a few days adding to your trip !
LF