I finally broke down and decided to do a stealth character to finish up the thieves guild achievements. Problem is I've heard this is the most buggiest of the guilds. Heard Karliah can stop the Under new management quest from starting. Also heard if I do too many misc quests to qualify for the city improvement quests it'll bug it so Delvin can only give out 1 of the 4 city improvement quests. So any help on this would be apperciated. Just wondering if this should went into the bugs section or somewhere else as I'm asking on both help and the avoidance of the gamebreaking bugs.

Well, until you run into a specific bug, I don't think anyone can really help you that much. When you do run into a bug, I'm sure those in the Bugs section can help you out.

Put the TG questline on hold until you get the city influence quests done. Save before taking Devlin's or Vex's quests, and reload if they're not giving you quests for the city you need.

One piece of advise I can give you: DO NOT GO INTO THE DWEMER MUSEUM UNTIL THE QUEST HARD ANSWERS! I met with Calcelmo long before I did the TG and killed his spider for him. He gave me the key to the museum so I decided to go in and check it out. Later on I found out that doing this broke the quest line where Karliah gets stuck in the basemant of the Frozen Hearth Inn.

In the final quest, Darkness Returns, be sure to make a hard save (not an auto) before you get to far along in the dungeon. Karliah can get rather buggy in the final part.

If you don't want to steal much, Vex has shill job quests that let you plant things in someone's home. You don't have to take anything. Also, if you do a Bedlam Job for Delvin, taking a unique gem will count for the quest, but it doesn't add to your stolen items count.

In general, do not revisit the dungeons you get sent to on the main quest line just to be safe.

As has been said, save frequently. I found saving each time before going into a different cell was very effective and minimised the amount of progress I have lost to bugs, crashes and glitches.

If you have any specific bugs, the forums have an abundance of information to help you.

I've had no issues with entering the museum prior to joining the TG. Based on my experience, you shouldn't have any issues so long as you enter before starting Speaking with Silence and don't go beyond the first area (where the Stone of Berenziah is).