I just started playing Skyrim, and so far I have just bought a copy of the original game for PS3. I have played for a few hours and finished a few quests, the last one being the killing of Mirmulnir. Do I have to finish the main quest before I get the DLCs (I'm thinking of Dawnguard, Hearthfire and Dragonborn), or can I buy them right away? Thanks.

Best to get them sooner, in my opinion. The reason being is that they will not only add things but also change some existing things in the vanilla game. So to better avoid, or have a better chance at avoiding, bugs and glitches related to these changes its best to have all the DLC you will be getting and start a new character then.

You can buy them right away! They integrate pretty seamlessly into the game. Plus you'll have access to handy new features like arrow smithing, new foods, boats to take you to the different port cities, and so on.

With Dawnguard, vampires will begin attacking towns once you hit level 10 - they can be a nuisance, but only if you fast travel a lot. If you're quick, you should be able to kill the vampires before they kill townspeople

Alright then, to the PlayStation Store we go.

Have fun!

Thankyou for your help.

I advice you to always save before visiting a city. In cases a vampire attack will cost some virtual lives of cool people.

Noted.