Ok, I'm a PS3 Skyrim player so hopefully, fingers crossed, I will be able to download and play Dawnguard in the coming weeks

What I would like to know is, from people that have been playing DG for a while now what are the MAJOR quest bugs/glitches that I can probably expect and/or try to avoid???
I've heard sooo many things about how bugged it is, but I really wanted to get a good idea of bugs that people have actually experienced themselves and not just heard or read about.
I have read things like if you start a new character the Companions questline is impossible to play if you side with the Vampire Lords, so you HAVE to complete the Companions questline before becoming a VL, is this true???
Are there any other questlines that bug out if you join either side in DG, such as the Thieves Guild, Dark Brotherhood or even the Main Story questline???
Would really appreciate your input.
Many thanks