I've been buying these for a couple of years at between ten and eleven pounds. The price rise coincided with 3's announcement of "4G at no extra cost". These are now not 'expensive 3G SIMs' but 'cheap 4G SIMs'?
Yes you can top up. When you put your sim in you need to follow steps to register. Every time you go on-line you will go straight to 3 home page where you can check your balance/ top up etc.. But what I do is buy another sim as it is cheaper. Topping up cost more per day than the pre paid sim. I have been buying the pre loaded sims for years. If its your first time buying, get a 3 dongle either on its own or with a sim in and data on. Then when runs out put in a new sim. I usually buy a few sims at a time(wish I had bought more last time due to rise from £11 to £21 for a 3gb). The 3gb work out best.
I really don't know .. I use for a mini iPad (a nano sim) & a standard iPad (a micro sim) .. If your laptop has cellular access & you can insert a sim I would assume it would be one of these. If you can insert a sim I think you should check with the manufacturer of your device what size sim it takes.