Thought I should answer properly...
1. Does IKEA in Poland take UK Visa or Mastercard credit cards? I'd rather not pay in cash!
Yup, shouldn't be an issue. Polish stores are very good with accepting non-Polish cards, unlike some other countries. The UK for instance is dreadful for accepting Polish cards :/
2. Would it be possible to get it delivered by a local firm from there to here in Berlin or would it be better to bring my own transport all the way from Berlin?
Should be nice and cheap to get someone from Poland to drive to Berlin with the stuff.
3. How big is the store, ie is it a huge IKEA which stocks everything in the catalogue or is it fairly small and always low/out of stock?
It's just had a huge extension built, so I'd imagine it has everything you could want/need.
4. How similar is it to the IKEA experience in the UK or anywhere else for that matter
Exactly the same, except the food prices are stupidly low. 1zl hotdogs?