I use the soldering iron to melt away plastic then use a razor blade to get the rest of the plastic off to allow a good contact. The entire connection doesnt have to be covered in solder, but needs to be on good to allow even continuity. I did end up getting a cheapo electricity tester because even though it was sticking good some of mine were not heating properly ended up they weren't getting full current.

As far as cutting of you turn the Flexwatt over you will see where it has little breaks. You cut it between the breaks. All pieces will need to be the same size if your daisy chaining them.

Also make sure you cover all the solder & wires with electrical tape, once powered it will give you a good shock if you have anything exposed.