For traveltimes you can use a Railplanner App :)
bestwise the local railplanners but atleast Scotty (from oebb.at) or DB Navigator (bahn.de) as these cover quite a lot :)

For London to Dublin you have to catch a train to Holyhead and from there a Ferry to Dublin (Irish Ferries offer a discount for Interrailer/Eurailer) https://benefitsportal.eurail.com/benefits/irish-ferries/

Please note that the Highspeed trains like the Eurostar London - Brussels (to get to Brugge) and Munich - Paris (one direct TGV per day) need a reservation that cost arround 30€ for the Eurostar and arround 17€ for the TGV

You may find cheap flights from Dublin to Continental Europe as you otherwise have to go all the way back to London to catch the Eurostar

Or catch a ferry from Rosslare to Cherbourg (France) and then onwards

THis site has much more info: seat61.com

You do NOT need now to REServe HTls at all-in fact on a populair site like booking many HTls only put their rooms in some 4-6 weeks advance. In populair cities there is such a huge offer that youll always find a place. IF you think the USA way (pricewise or the like) then you have to broaden your mindset

The 20th cent style of doing train-ferry-train will bring nowadays only diffculties and stress. Most ferries do not even take peoples without card anymore.

Thank you so much.I m not sure nos to buy the pass.Because it Is difficult to know the Time table to book Hotels.May I Will keep on travelling by plane