My main question is, how difficult is it to sell a RHD car?
You've got two choice, do as Monitor suggests and get the steering and all that's connected with it changed, or sell it in the UK.
Mate, do not try to sell it here, you can go to Polish eBay (Allegro.pl) and you can find tons of UK reg cars for sale for half the price of a left-hand drive. You won't get anything near the current value of the car. My suggestion would be to sell it at home and buy a car when you move here. Car are reasonable prices and insurance is dirt cheap compared to UK, here you insure the car and not the person. MY insurance on a 1.8 Focus was only 1300zl, that would be around 270 UK pounds-ish.
Moving your things can still be done pretty cheaply, there are many white-van man types who drive to Poland weekly who would transport your belongings, check out sites like gumtree etc to try and find some. When I moved from Ireland I hired a guy and it cost less than 100 euros for a van full of stuff.
Without Polish you will find it extremely difficult to find a job. Krakow, especially, is awash with people who fell in love with the city and moved there. You could teach for a while, until you find your feet and build up a list of contacts. But you will need at the very least a CELTA qualification. But I guess you could finance this by selling your car?
Don't want to p!ss on your chips man, Poland isn't an easy place to live without the lingo or the qualifications to get a job.
The likes of Google/IMB are relocating here as we speak, but they will be hiring Polish people who already have 2, if not 3 languages and Master's degrees in IT/Finance etc.
If I was you, I'd do the CELTA, teach for a couple of years, build up tons of contacts, try learn some of the lingo and then get back into business thru the people you've met on the way.