I'm starting a new game and wondered if it's possible to avoid triggering the random dragon attacks, in the same way that it was possible to avoid triggering the appearance of Oblivion gates in Oblivion. If so, what is the exact point? I'm just curious and in no way whining about dragons

Ye it is, just dont do Bleak Falls Barrow, avoided that quest for the first 20 levels and I was able to explore and everythign without those pesky dragons

Dragon attacks begin after you hand the Dragonstone over to the mage and you get called out to the western guardtower.

most specifically you can retrieve the golden dragon claw from bleak falls barrow and turn it in to the shopkeeper in the Riverwood Trader, just hold the dragonstone that the mage in Whiterun asked for and you can hold that chain.

Worst thing is having the stone in your inventory and visiting the mage room in Dragonreach triggers the entire conversation
I was just trying to use the enchanting table but it triggered the conversation

Ahhhh... damn. I already handed the dragon stone over

Is it still possible to buy the house in Whiterun without starting the main quest?

You can complete the Golden Claw quest, as well as getting the dragon shout from Bleak Falls Barrow and killing the boss at the end. The trigger is handing the Dragon Stone over to the Yarl's Mage. (I forgot his name,)

You should be able to back out of the conversation if the mage walks over to talk to you and leave the quest for later.

No, you have to defeat the dragon to become thane.

You get the chance to buy the Whiterun house right after the Jarl of Whiterun tells you to meet his housecarl outside the city to investigate the attack on the western tower. So you don't have to be Thane of Whiterun to buy the house.

In theory you should be able to buy the house and still not trigger the event at the tower when you avoid leaving Whiterun on foot (instead only use fast travel). But that would maybe mean you can only enter and leave Whiterun by fast travelling.

But I honestly don't know where exactly the tower happening is triggered. When you get close to the stables in Whiterun? Or do you need follow the soldiers up to the tower?

Maybe you should save the game and then fiddle around a bit to figure out when exactly the tower thing is starting. Then you would know and could load that save to take it from there

"Is that a dragonstone in your pocket or are you just happy to see me?"