No big problem going to the IoM.
It's the same as any other Class D airspace, make sure you have clearance to enter before you do! But they will have your flight plan and will be expecting you.
The handling issue is a problem at any airport that deals with commercial traffic these days. If you want to park in the Restricted Zone (i.e. outside the terminal) then handling is a must as someone is required to escort you to/from your plane. The handling agents there are set up to handle airliners and charge accordingly. Airports get round this by having separate parking areas for GA outside the Restricted Zone, but these often involve a long landside walk to the terminal. At Ronaldsway Manx Flyers provide this service, but their facility is on the opposite side of the airport to the terminal. Of course they can charge you what they like to use their parking.
I have heard that you might be able to park at one of the maintenance areas which are closer to the terminal, but don't know who to contact or what they would charge, otherwise it's Manx Flyers.
If you divert to Andreas then Special Branch might get suspicious, remember to tell them that you are going to/from the IoM.