Seresto does not kill tapeworm

This would provide 7-8months of protection from Ticks and Fleas. Not mosquitoes

Yes you can use Seresto and Stronghold Plus together.

According to the manufacturer - Bayer - the collar is non-toxic but it can cause an upset stomach if it were to be licked.

Yes, the collar will break away. Seresto has a double safety-release mechanism, so in the unlikely event of your cat being trapped, the collar will widen when she gives a hard pull, allowing for a quick release. The collar is also built with a predetermined breaking point, so a harder pull from your cat will break it.