1. No idea. I found one that isn't the OEM size, but barely fit. I had to take the inner bracket off to get it in place, which wasn't necessary with the battery it replaced, and it fits with less than 1mm, but it fit.
3. No. Most batteries are made by just a few major companies. I'd buy any one of them. The way to make it last longer is to either put it on a battery tender, or use a switch to disconnect it if you're leaving the car parked for a long time. Also, make sure there isn't a parasitic drain (aftermarket OEM radio integration kit or something) that's killing the battery.