I've started a new game of Elder Scrolls and I know that once your character hits a certain level the vampire attacks start whether you want them to or not. This is bad game design the attacks shouldn't start till you are ready to do the quest. I might not even install the DLC content again and wait for awhile before buying the next content till I know more about it and how it will affect the main game

No need to uninstall. Just disable it in your Data Files list when you start a character. When you're ready to play, re-enable it. If you consider it bad design, this is the best way around it and it's how I play it.

i'm playing on the Xbox 360 I can't do that

Ah. Well, I feel the same way you do about the way it starts and if I were on a console, I'd delete it too.

I'm playing on PC and have decided I won't load Dawnguard until I'm ready for the quests. This was because I started a new character for Hearthfire who came back to Whiterun after killing the first dragon to find death and destruction (incl Adrianne dead) due to a vampire attack. And another vampire attack and another - they were almost every day. Nice to collect the inventory from the dead but not so nice to have to deal with the vamps when you're low level.

I just started a new character on Xbox some days ago. And i only have Hearthfire installed.

The moment i'm ready to tart with Dawnguard i'll position my character at Stendarr's Beacon, save and exit the game and then download Dawnguard.

I have decided to do the same: delete DG until I am ready to do the quest straight through. I waited until I was level 40 and had already done a number of other quests and finally reinstalled it. I probably will never start a new character again with DG installed.

I think this is the method I'm going to use. Beth won't fix the bugged start conditions or the fact that vampire raids happen when you aren't anywhere near a cell. I was down in The Rift when vamps depopulated Whiterun. Yes, in a seperate instance from the one my thread was about. And yes, both time it was vamps, I had the ash piles to prove it.

I'm on 360 so I'm deleting Dawnguard until I'm ready for it.

Will there still be vampire attacks after completing Dawnguard main quests?

This is so bad, OMG.l.

If i was to answer that fully the thread would get moved! I suspect you know the answer anyway.

From my experience, vamp raids on cities end once you are done with the MQ unless you blot out the sun, and then only for that day the sun is blotted out.

I guess I lucked out with my character, only one Vamp raid on any hold so far and I reloaded a previous save to clear that.
Not sure if this is helping but I never fast travel and never enter a hold or village area until mid day. I just wait out in the wilderness away from the area until daylight.
Started doing this after fast traveling to Riften to find a pack of Vamps had killed practically everyone.
Like I said I might just be lucky so far.

it never bothered me to tell ya true, usually just three dudes showed up at lower levels and proceeded to get mauled by the town guard. I play on the default difficulty, so maybe that factors in, but i never lost a named npc.

unless you have a bug. then the suspected answer isn't true anymore! xD