Something to keep in mind about time needed for gaining cleric spells... you have to have a party willing to stop for however long it takes to pray for those slots. If you need them in a situation that is time sensitive, you're not going to be able to use them until you can find a place safe enough to pray.<br/><br/>I'm not saying that it's a bad idea to keep a spell slot or two open, just that time to pray may not be abundant if someone doesn't want to stop for it. And, I'll hve to say that you can't do it while riding or walking.<br/><br/>I'll leave the question of party origins up to the players. If you want to have a previous interaction with someone, or everyone, you're free to work that out. If you want to be someone new stepping in, that's ok too. I've learned that when I ask for a party that is already established, I get at least 1 who insists on being "the new guy."  So, as long as no one pulls the "I don't want to be here." or the "I'm only here because I have to be." card, I'm giving you complete freedom to decide for yourself.