The search function could come handy and even answer your question(s) next time

The one below is just one of the countless threads concerning bag/seat on LOT:

Checked bag allowance for Star Gold on economy saver

In a nutshell: 1 bag indeed allowed for Star Alliance Gold members but no seat selection (unless you’re willing to pay for it, needless to say).

That aside, no issues with weight/size at Warsaw (make sure to join the priority lane, worst case scenario —i.e. Dash operated flight— they will give you a Delivery to aircraft tag), you could however encounter problems when departing from an outstation (Venice is bad, Belgrade & Zagreb also were pretty thorough, just to mention a few airports I recently visited).

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