If you travel on this bus, then please don't forget your passport/ID as you will cross the border. The border officials make random checks. Unlike the Swiss/Liechtenstein border which is no working border as such, here you have a proper border with customs buildings on both sides. Actually the Swiss border guards are manning it, so it's in fact a Swiss/Austrian border instead of a Liechtenstein/Austrian border.
The bus line no. 14 brings you fastest to Feldkirch in about 24 minutes. They run hourly at least but not on weekends. On a Saturday you have to take the slow no. 13. On a Sunday there are very infrequent services by the Austrian OeBB rail company.
If you have a car then you can of course see much more of this small country in one day. The main roads are excellent and the signs very clear. So if you have one at your disposal and not much time, then it's worth considering it.
If you travel by bus it is actually not only "to" but at the same time "around". Schaan is a crossroad as there are several bus lines going through there. Line no. 12 takes you either from Sargans (Switzerland) to Schaan every hour or from Buchs (Switzerland). We walked to Schaan from Vaduz but then took the bus to Feldkirch.
The main bus station at the post office has a public toilet round the back of the building as well as two ATM's.
Only slow trains from Feldkirch, Austria to Buchs, Switzerland stop in Schaan, the station building seems to be closed