How do I start the main quest?
Kill a dragon.
How do I join the College of Winterhold?
Get to 25 skill in any magical skill tree, then speak to Faralda at the college entrance. (If she isn’t there, press the doorbell, by the ramp)
Why can’t I obtain the Dragonstone?
This quest is auto completed when you kill a dragon.
How do I become the Thane of Whiterun
There is a new way of becoming a Thane of Whiterun. Complete “The Blessings of Nature” quest (Danica by the Gildrergreen tree to start) and talk to Jarl Balgruuf when the Gildergreen tree is repaired\the sapling blooms (note: this requires you to complete any other quest to simulate the passing of time). He’ll thank you and allow you to do the standard thaneship quest (help the people of the hold).
You can buy Breezehome before this at a much more expensive price, but unless you are thane you do not get the housecarl.
I can’t start the Thieves Guild through Brynjolf!
Thieves Guild Requirements is included in the list, which requires a certain amount of pockets picked/items stolen. Check the requirements in that mod’s MCM.
How do I start the Dragonborn questline?
Dragonborn content is available after completing “A Blade in the Dark” during the Main Quest.