I've always brought a light pair of long pants, light coloured, not tight (dark attracts mosquitoes etc more) for bug protection, cool evenings and for off bike activities.
I also bring tights that I wear often when riding when it's cool and or for sleeping.
I also bring rain pants.
Could I eliminate the long pants? Sure, but I like a pair of regular looking pants on long trips, very handy for off bike stuff which along with a light button down shirt sleeved shirt is very versatile for looking and feeling non bikey --nice on a really long trip.
My pants are one piece, I'm not crazy about zip offs, but be aware of the huge difference in weight between these types of pants. Some are twice as heavy and the volume of others.
Kinda last minute on choosing your clothing for a long trip, but I get it, We've all been there.
With all clothing, I'd prioritize weight as much as you can budget wise.