I'm wondering if it's ok to bring some scotch as a gift for my potential business partner?
No. Unless you know them. Poland does have high levels of spirit consumption however it is also more puritanical than you might have heard about alcohol. In any case, your business contact might be a sober alcoholic going to AA meetings and who smashes the place up after one sniff of a wine gum.
If you want to bring alcohol, try a couple of bottles of good (very good) English wine.
My another doubt is about kissing the woman's hand... A friend of mine told me it's customary in Poland...s
Don't do it - it's old fashioned and would look strange. It's mostly done ironically nowadays or by the over 85s.
shall I hold the door for my female friend or will it be taken as an offence?
No problem holding doors open or not holding them open - Poland is just the same as the UK in that respect.
Wait until you come and play it by ear.