I used to learn Japanese by myself, and did the same with Finnish for a short while only. I agree that your goal is a high one for THIS summer, probably too high. Best bet would probably be one of those phrase books for travelers, and expand from there. Those are topics that you will need, most probably.
For the longer run, I would suggest to invest into a book, where self-study is possible, or even the main goal of the book. The material on the internet is great, for an introduction, and as side-material. In my opinion a book gives the structure, and a lot of additional information, and exercises, most sites do not give. The one I would get at the moment is probably
this - watch out that you get the version WITH CDs.
Besides a book I strongly suggest to find ways to actually use the language, preferably with native speakers. Two sites that I use for that are livemocha.com and mylanguageexchange.com - they ask a small fee for subscription and then you can get in contact with all kinds of people learning, and helping all kinds of languages. It is usually an exchange, so they may want to learn your language, and offer Finnish as exchange. On MLE you can get in contact actually without the fee, but can only say Hi, and hope the other person tells you their email, or some such thing. In case you are playing computer games (MMO or whatnot) why not choose a server where the Finns are playing.
And now that you will be traveling here, indeed, talk talk talk

I am one of those shy ones for whom that is not so easy, so I take myself by the nose here, as we are saying in my language

Maybe you will be making friends here, where you can exchange addresses. Have a great trip, and enjoy!!!
