Finns love to take tours of Åland by bicycle and using the ferries. You can camp or stay in cabins (cabin/cabins= "stuga/stugor" in Swedish), there are LOTS of these in Åland and ones with breakfast & showers/WC in a main building are pretty cheap but quite nice. Remember that many overnight accommodations will include breakast and even with cabins like these breakfast may be grattis (free) or a very cheap option. You can also cruse and island hop by car or motorcycle but with bikes (motored or no) its easier to always have find room on the ferry. I don't know all the sights there might be on the islands, but at least Kökar has a lighthouse. This map show the lighthouses ("majakka", plural "majakat") in Finland http://www.lighthousetourism.net/seminaari/Suomen_majakat.pdf
The Åland meritime museum is also fantastic.
On the mainland Turku castle is nice, but honestly Stockholm as more to see than Turku or helsinki. My #1 in Stockholm is the Wasa museum.
Babble Swedish might get you a handful of words for your trip.