I will be buying land
Ok, that is a different story. Foreigners cannot buy land before 2012. The exception is up to a total of .5 hectare (1.25 acre) of land for residential building purposes. Agricultural and forest land is out of the question. Your Polish spouse should be able to buy any land she wants, but not the 2 of you jointly.
I am already pre-qualified for a mortgage by a UK mortgage company.
It is very difficult to get a mortgage in Poland for pure land. So typically if you find a nice plot of land to build a house on you must pay for the land in cash, then get the mortgage to build a house. So make sure that the UK mortgage will allow you to buy land.
I am looking through allegro
Try gratka.pl/dom
Permit process - for the apartment / house permit it should not matter that you are not resident. Pretty much just a formality
Estate Agent - Poland is a big town. What region are you planning to buy in? If you are still serious about buying land, you may want to contact these guys: plotspy.pl I have never used them, so I can't vouch for them.
Good Luck