Looking for recent experience. I booked a flight thru Iberia operated by Veuling

I have 1 piece of hand luggage and 1 underseat bag allowed.

1) are they stricter on the underseat size or the overhead luggage size?
2) will they require me to weigh my underseat luggage? That will be my heavier bag (though smaller)
3) can I book an online piece of checked luggage at a discount right before boarding if needed?

thanks!

my flight is mid-Sept Fri morning direct out of BCN.