Yes, completely separate and use alone ok

Yes. Easily done

yes - you can split the paniers no problem

Yes. The panniers can be independently mounted of each other.

yes. they pop on and off in a flash, and i've often used just one. if your gonna be carrying alot of gear in just one pannier, it may be advisable to split your stuff into two half full panniers though, as alot of weight on one side may effect your steering. Having said that, they're not massive, so even a full one shouldnt weigh that much. unless your carrying lead or rocks !

They have a handle, but no strap

yes - a small very basic handle

There is a small strap at the top of each bag.

theres no carring strap/ shoulder strap. They each have a handle fitted on the top/backside, which can be fastened together with a big press-stud, you can carry one in each hand or both in one hand

yes it's a pair of paniers

Yes. You get left and right panniers

I think they're universal, yes. theres two clips on the top which snap onto the top bar of your rack, and an adjustable/ sliding arm lower down on the rear to hook onto the nearest down stem. the arm is reversible and locks into position with a screw driver. once you set it up and lock it in position, you dont have to use the screwdriver again, it just pops off with a little shove.

There is a poppeer, like on the front of a jacket, but it doesn't hold any weight