It's continental so it's more stable, high pressure dominates frequently (comparing to UK/Ireland), but in summer time you have to watch out for thunderstorms.. not a big problem.
I wouldn't focus on Poland alone, there are loads of schools in Czech Republic, Greece, Portugal, Spain etc, google is your friend
before you even start doing anything, just grab an intro lesson - see if you like it at all or not.. Also get your medical done just to see if you are fit enough. No point in building dream castles if you haven't got your foundation in place... I've seen too many people dreaming big but failing at the basics, so make sure you're not one of them before spending any money or making any big life decisions