Crim, The Red Thunder

quite the contrary, i am often a guildmaster before really starting the main quests. There is no limit to what you can do before completing the main quest, the only useful aspect of the main quest to acheive is earning the immunity to disease. Past that, i have had characters completely abandon the main quest, and do the guild quests for fun.

Not everyone in the legion attacks you, only talos cult members (theres a few more besides oritius, IIRC... just not everyone.) BUT! You can't have a bounty on your head that makes legion members hostile. Secondly, i would recommend invisibility after clearing out the cult room, and killing oritius. Just to be on the safe side. I didn't need it, and to this date, the legion isnt hostile to me (of course, this is some 100 days later, but even then they weren't hostile other then talos cult members...)