Also can I sell some land owned by 'company' to myself 'individual' - what is the best tax efficient way to do this?
Yes you can, but you may need to pay 23% VAT. You need to check with an accountant.
what is the quickest way to sell a ready made company in Poland, how do I go about this? It Is registered in Gydnia but trying to sell the flat that its registered to.
If the company just uses the flat as its registered address but isn't the owner, just move the company's registered address somewhere else. There are plenty of virtual offices around that will provide this service for a small monthly fee. Selling a Polish company that has had a trading history is a complicated business, especially if it's had employees in the past - you have to keep their records for years. If it's not trading, it's much easier to close it down. Again, talk to an accountant.