Hi
@seaseeker how exciting for you. I can’t speak to how things are on the Norte right now - as to numbers and accomodation given covid restrictions - maybe some forum members who are there will reply. But usually late September would be a popular time and you’d be sure to meet some fellow pilgrims without feeling crowded.
As to weather … well it’s always a gamble. But I wouldn’t be too concerned about the gaiters or rain pants. There are whole threads on the forum about the pros and cons of waterproof pants. My observation is that the majority (though not all) think they are not worth the trouble. I’m in that camp. Some (including me) prefer to walk in shorts most of the time and especially when it’s raining. Your legs will dry quickly. Different matter in winter / snow etc but in late September / October, I think you will be fine.
Final thing - if you have a spare few hours in Irun, I highly recommend you walk the couple of kms to Hondarribia - even just to wander for a few hours. It’s a wonderful town - and would be a shame to miss when you’re so close. You will also see shells and Camino markers there as you can start the Norte from Hondarribia or Irun.
Have a wonderful walk. Take care. Buen Camino.