hey there
first of all - you'll be fine.

As you said Polanica Zdroj is one of Polish SPA cities and one thing you should be doing over those 2 weeks is relaxing. Long walks in the nature, long sleeps, fully loaded Kindle would do. Take a camera with you - that area is super scenic.

There are quite a few grocery shops in there (mini Safeways) so you will be able to use your google translator.

Good question about cash - it might not be a bad idea. I would avoid carrying Benjamin Franklins, but just take your debit card and use ATMs.

One thing I probably did not understand - are you trying to drive from/to London somehow?

mfk