There is 1 railway line in Liechtenstein, which is operated by ÖBB, Austrian railways, which is included in Eurail/Interrail.

To determine how many travel days you need, it's better to make a plan with timetables yourself, e.g. using the Deutsche Bahn planner, and then see how many you need.

I think you can buy Interrail or Eurail. The prices are normally the same but Eurail has no limitations on travel in the country of residence, so that could be an advantage.

Liechtenstein is Part of Eurail BecAuse the railways line infrastructure belongs to Austria But trains stop only Mo-Fr in Liechtenstein and the Station Schaan-Vaduz is quite a long walk away from the capital Vaduz.

better to go to Sargans, Buchs or Feldkirch and from there take a bus (not included in the pass).

7 day pass will be the best for you if you don’t want to buy lots of single tickets (and I don’t think That would be cheaper overall)

So you don’t plan going by train to Paris from Sweden?

Do you plan to travel a whole month? Then it might be wise to have a bit of extra days, in case you’re fed up with the (bigger) cities and you just want to enjoy and chill out in nature somewhere out of town or get away from the busy cities. Plenty of mountains with good scenery for hikes, or winter sport possibilities on your route, depending on when you go. But that depends on your own travel preference of course .

If you buy the Eurail and if you would happen to have one or two traveldays left over after your trip, you can use them to visit other places in Sweden and get the most out of your pass and save you some money. With interrail you won’t have that option, since you reside in Sweden. And Sweden is a big country, so more difficult to get abroad to use those remaining days.

A good tool to help you decide which pass suits you the best is this one:

https://www.interrail.eu/en/interrail-passes/choose-right-interrail-pass