A) All DLC that released before DA should be in there tho they are in shops and on quest boards so you'll still start with pretty much nothing
B) don't be ashamed to run away! a lot of the enemies you can not kill at a low level, so pick you fights. the rest is basic RPG, don't forget to buy to weapons, upgrade your pawn's equipment as well, buy new skills and stock up on healing stuff before you go on a mission.
A) Was there any DLC that came with a new purchase that I will be missing?
B) Any tips or hints before I start playing?
A) Nope, so no worries.
B) Near the beginning of the game, after the first few main quests, you'll be directed to go back to Cassardis to search for Quina, and then after getting the quest in Cassardis, you'll need to go to a place called Witchwood. The way there may be troublesome to you because there are a few strong enemies. However, that quest is quite important in opening a new area in the future, even if it's a side quest, so it's recommended not to miss it (it's easily missable if you continue the main quest, since it will cancel it).
Don't worry about "when" you'll get the quest though. There's a scripted event that will tell you "hey, have you seen Quina?" to give you a nudge that the side quest can be gotten now.
If you have trouble fighting the enemies before reaching Witchwood, I recommend either running pass them (don't be afraid to do so), or rest at Cassardis until night. The strong enemies in that particular area will be replaced by wolves, which are much easier to kill. However, Witchwood itself will be harder to navigate due to being at night.
C) Have fun! Don't worry too much about stats growth and just try to play the way you'll like, especially in the beginning or at least the first playthrough. You can always try asking for tips here if you feel the need.