Some will disagree, but assuming your Polish postal service is reliable like here in Australia, I’d go for a paper pass. 

If you live in Luxembourg, then that is your country of residence. That has the advantage that the max. 2 travel days in your country of residence are not really a limit, since public transport in Luxembourg is free anyway in 2nd class.

Please do no plan with the app, it s not reliable. And if you want a paper pass, just buy one from the ticket office. Then you don't pay for delivery and you have it immediately.

Re your point on registering each journey, I am afraid that is the case with mobile passes, and I believe even with paper passes.

If you go for mobile passes they can all be loaded onto one phone and then journeys can be added to each trip in one go and easily changed if needed. You still need to transfer from each trip into each pass individually (a few seconds) and show them individually from the single phone when inspected.

Although I haven’t used a paper passes I understand you will need to write each train details into each pass.

For trains requiring reservations you can buy for all passengers at the same time, some operators issue one reservation document per passenger and some will simply issue one document for all passengers.

Dzien dobry-Perhaps-if you live close by and pass by anyway-ask at LUx Gare if CFL is also still able to sell the Paper passes (we would also like to know for any furhter questions)-and if you really prefer those, and CFL cannot do, then hop over to Trier (3/single extra to pay) and buy there on the spot by DB. In that case you will need proof you do live in LUX (aufenthaltsgenehmigung). It may prevent problems if you also intend to travel a lot in PL on PKP/PR-as this is where problems may arise if they see you´re POlski. (otherwise would have max 2 days of travel there). NOT valid on other trains, like KM, KS, WKP etc.

Those ferries are not included-but most give discounts-and some are still quite cheap between SE/FI. Stena does a lot of them, also Silja/Tallink and Viking, most take the discount ´eurail´ as enough.

According to their website they do.