For your mage lords, they won't be physical guys, that's for the poor and lowly hirelings. You are most likely not going to be religious, for they pretty much think only of themselves, have no real qualms about necromancy, and usually are a lot more reckless with their experiments and magic. The mainland Telvanni are quite xenophobic, as compared to the ones in Vvardenfell, and all Telvanni believe in the principle of "you don't bother us, we won't bother you." And it's not that they believe that killing is okay, as long as you are not caught, it's more like if there is an argument or some sort of conflict, and you kill the person you are in conflict with, your argument was clearly superior. Failed test subjects or minions dying from accidents doesn't matter since they're too below you (literally and figuratively once you have a mushroom tower). It's Hlaalu that states it's okay to steal, as long as you are not caught.
Here's what the recruiter says when you ask them about the rules:
"We trust all members of House Telvanni to use their own judgment. If you steal from another Telvanni, but still live, then clearly you deserve whatever you stole. Murdering your opponents by magic or treachery is the traditional way of settling disputes. If you win, then clearly your argument has more merit. You may be expelled as in any other Great House, but most Telvanni will not care or even know about it. Does this appeal to you?"
With those rules, it pretty much allows a myriad of personalities to enter, usually more crazy and eccentric though. Talking with most of the mage lords and their magical underlings will give you a good idea of what they're like.