as far as the thieves guild entire quest line, stones aside, the misc questline can be completed in a hour or less. You just keep getting jobs that are the same city. You get a job and theres two citys, focus on one and then refuse the job from the person who job wasnt the city u wanted and accept a new job, rinse and repeat. not breaking the system, its soemthign i woulda doen in real life.
there were no guilds in skyrim, just grps of people that u had to save the world again from.