As a Pole I feel obliged to comment on this one. I was raised and pretty much lived me entire life in Warsaw (now studying in London) and have tons of friends doing medicine in Warsaw.
1. Yes, this option is by far cheaper that any other you listed. Flat on Warsaw will cost you at most 250 euro a month, probably even less. Other prices:
eating out: from 3 euro (a kebab/street food) to 10 euro (a restaurant), I usually around 4 if you know where to go
alcohol: bottled beer is around 1 euro, excellent craft beer costs around 3-4 euro in pubs, 0.5l of liquor - 7 euro
cinema: 5.5 for a ticket
public transport: with a 50% student discount its 13 euro for a monthly ticket, single fare is 50 cents, a cab is 5 - 10 euro.
Oh, and if you are German then I don't think you'll pay any tuition fees.
2. Workload: I believe you'll be working far more than on any UK university, at least comparing year 1 experiences. This is both bad and good. Yes, you do learn a lot, but much work is cause by lecturers not specifying what they expect you to know. You should be more confident with studying by yourself than expecting any help. You don't see Polish medics partying too much during the academic year (as opposed to those in the UK...).
3. Language: practically all young people, especially at uni are fluent in English, in general I don't think language will be a problem at least in Warsaw (or other major cities). Not sure how good university staff language skills are, I would advise you to talk to a student from the university you are applying to to make sure they manage. Polish language is tricky, but only the grammar. You'll learn to understand it quickly, but possible never to speak 100% grammatically correct.
4. Student life: now this is a bit tricky. As opposed to the US or UK, Polish unis have a different idea of student participation. There are unions, but their prime goal is to represent the student voice, they don't organise clubs and societies. There are clubs, but mainly to allow you to expand academically (e.g. learn programming artificial intelligence if you are doing computer science or engineering). PE is part of the curriculum, its rather elastic, so you can either participate in sth that the uni offers or be part of a professional club somewhere else. Frankly, at least from my perspective, it more like "uni is to study, you can organise leisure by yourself". Is that bad? Must sound horrible to any Brits reading this, its pretty obvious to us, though I haven't experienced it, so I don't know. I can add that Polish people (students especially) are really friendly, as a foreigner you'll be flooded with questions on every party
In general, I would say your experience could be very good or very bad and I can't really tell which one is more likely. I moved to London cause my course is awfully taught at Polish unis and I got into a really prestigious one in the UK, but that doesn't mean education in Poland is bad. I would say there are a few courses where you'll get decent education and I do believe medicine is one of them. Its gonna be tough, but you will be very knowledgable by the end of your diploma (oh, and this will be much sooner than in the US). I did consider medicine for some time and, unless I got into Oxbridge, I would likely stay in Warsaw. After uni you would probably prefer to move abroad, cause the healthcare system is such that you'd be underpaid for a while (sad but true, just being honest here). However, I guess you plan to do it anyway, so its not an issue.
Feel free to ask more questions or PM me