The pinned topics here include the latest rulings by Bull, ultimate super-GM of Missions.
He noted you can have as many calenders as you want. Just keep in mind that you can only have 4 weeks of downtime after each run.
Contacts in Missions do not use their stats, and I do not recall any statement over at SRU that they would. I noted myself there that Missions uses its own special rules, which are Connectionx2+Loyalty and buying hits. Note that you can buy bonus dice by paying more, before hits are bought. So do not divide by 4 until bonus dice for paying more are added. (Such as +50% on a 5/4 contact for 16 dice = anything below availability 20.)