Rossko
I hate to disappoint but your biggest issue with Isle of Man will be getting there. Ferry space and to a lesser extent air seats like hens' teeth and ferry company is known as the Isle of Man Steam Racket Company. They operate routes from Belfast, Dublin and Liverpool or Heysham to Isle of Man.
https://www.steam-packet.com/ Spaces book up in advance as in you may find a few available but there is a waiting list. Do some browsing and see what you come up with. Going as a foot passenger might be an option as transport on the Island is good.
Last year coming back on the ferry from France to Rosslare there must have been close to 1000 bikes on the ferry, many heading to Isle of Man for TT.
Accommodation is scarce there and you would have to do some chasing. Rip off culture exists there as in most places at times like this so be careful.
I have a brother over there but don't venture over for TT although it is an amazing experience. Its a lovely place to visit too.
Fly Dublin to Isle of Man with
www.aerlingus.com but check out
https://www.manxflights.com/airlines/ from UK airports.
Check out
www.etihad.com and
www.emirates.com as well as the usual suspects for flights from Australia to Dublin via Abu Dhabi or Dubai. They also offer to London and most capital cities in Europe.
Four weeks in Ireland and UK by car sounds good. There is a good ferry service between here to UK and France.
www.stenaline.com www.irishferries.com www.brittanyferries.ie [France only] are your options. France is about 14 hours and all are overnight services with decent cabins. Irish Ferries offer midweek services to France and they are good value in June. Brittany Ferries do Cork Roscoff and little to choose in terms of price between their PontAven ship and the Irish Ferries' Oscar Wilde- both are excellent. Irish Ferries and Stena Line also have an economy service to France if you fancy going in a punt. Ferries and flights between Ireland and UK are many in number so no issues anywhere in getting bookings. Ireland/UK ferries are excellent too. Don't forget Belfast across to Scotland and take in some of Scotland. No real need to book these far in advance. There are some early booking offers but you are better to stay flexible for now.
Malta sounds rather nice too...fly from Dublin?
www.ryanair.com fly 5 days a week, not on Tuesday or Friday. Horrible airline but reliable. I didn't check from UK but they fly 11 UK airports to Malta.
If you have a month tootling around Ireland and UK you could have a nice trip. Camping or hotels? Hotels are a good option at that time and there are some good chains too.
When things are more defined an Eccentrics meet up might be on the cards. I have already floated the idea of some Kamping Eccentrics at the beginning of June and signed up for a bike camping weekend in Northern Ireland for 29th April.
As Bill said you can pick up a car over here but both UK and ourselves use
right hand drive so if only driving in UK and Ireland maybe you can get that option. If you fancy some K or bike trips the insurance is an issue but 88KE has details for sorting that out. I drive lots in Europe where they drive on the other side and always take my own car with me. Easier for me when the car is at least familiar as in steering wheel on the right.
Going around Ireland check out
http://www.wildatlanticway.com/home/ it takes you round the coast of Ireland. It doesn't take in Northern Ireland but you should not miss the North Antrim Coast and down to Belfast and Strangford Lough. Amazing stuff. Dai and Comberjohn and Markzz and GCMcQ are in that area and Ringfad is from there too, extremely hospitable so you would have a nice meet up.
In UK south west is really nice, especially down into Cornwall. Minack Theatre, Eden Project, St Michael's Mount...to name but a few.
Check out Irish Ferries for deals from Rosslare to France, you could do Ireland Rosslare to Cherbourg, take in the WW2 landing beaches and war memorials, go west to Mont St Michel which is really worth a trip, then take Roscoff ferry back to Ireland or take a ferry from Roscoff to UK south coast. Or do it in reverse.
So a thought.....start in UK, head to south west, dip down to France for a few days...back up to south coast of Ireland, take in coastal route, back round to Belfast, round to Scotland......back down to arrival point. Park somewhere and head to Malta.....
I am sure lots of communications between now and next summer..........have a good chat with Gaz80 because they moved around quite nicely.
That might get you going......