1950 zl
You would not be able to survive at all on that much, live like paupers on twice as much, and would require at least three and a half times as much (7000 net) to even consider taking the job. Those wage averages you find on the internet are worthless as far as you are concerned. Ignore them.
Your apartment alone is going to cost between 2000 and 3000 PLN, all fees and bills included, and
A LOT more if you are talking about amenities like club house, sports club, health club. Very few Polish apartment complexes have such amenities, and those that do are definitely in the luxury range, and very, very expensive. May a little cheaper if you are willing to part with convenience and comfort. Basic groceries and household expenses and very frugal entertainment are going to cost you between 1000 and 1500 PLN a month, and more if you like to eat out in good restaurants, go to health clubs or country clubs, and live an active social and cultural life.
Your wife will almost certainly not be able to find work after you move here. If she wants to work, ask the company that's hiring you whether they can arrange something for her as well
BEFORE you come. Otherwise, make your decisions based on the assumption that she will definitely not find work. She would have to have extraordinary qualifications and experience to find work on her own in Poland, like lots of SAP or HBase experience, and then, while she may find work, it may not be in Gdynia.
7000 PLN net should be the very bare minimum you should accept, and only if you are truly desperate. 10K net would enable you to live quite comfortably, but you have to balance that with the reduced opportunities for advancement and reduced absolute savings potential compared to Western European and English speaking countries. And the fact that your wife will probably not be working.
Like I said, working in Poland will probably do little to further your career compared to working in the West, and opportunities for enhancing your qualifications through continuing education are limited. Disabuse yourself of any thought that working in Poland will be a foot in the door that enables you to move up the corporate ladder or make useful contacts. Like I said, most jobs you will find in Poland for companies like IBM are essentially dead-end swot jobs that are "internally outsourced" because no one in the West wants to do them. Employee advancement and improvement are not company priorities. The corporate types that hold the keys to advancement will probably not even be aware that you exist, and getting their attention will be very difficult indeed, if at all possible.