What mods would you recommend for a first playthrough ?

Play Vanilla, I would even recommend turning off most of the DLC. The games is most cohesive in it's original vanilla form, much of the later DLC is VERY poorly integrated

Stone prisoner being just about the only DLC that was well integrated into the game.

Qwinn's Unofficial Fixpack is a nice thing to have. Other than that I can't really say much is absolutely needed for a first playthrough.

As far as mods I am going for a couple of visual enhancements,the UI Mod,some gameplay changes"Like Lockbashing",Restoring Cut Content,and Bug Fixes.I am considering Improved Atmospheres but good just looking the install instructions is making my head spin. My rule of thumb for mods tends to Bug fixes, Additional content including restored content,game play changes that I think should have been there,but don't break the game and some visual enhancements if necessary.Always keeping Lore Friendliness in mind.

Not sure, if this a cheat mod or a "the way it should of have been" mod. But I have always used the Extra Dog Slot mod. Makes Dog a summons (like DA2), not occupying a companion slot.

http://www.nexusmods.com/dragonage/mods/664/?

I recently played the game (Origins) and used the following mods (Available at nexusmods):

Sigrun_Law_Order ( www.nexusmods.com/dragonage/mods/3001 ) To Fix a possible bug in the expansion of the game (in a single quest).
Silverite Mines Equipment Glitch Fix v1.0.2 Probably the most important fix for the expansion (NASTY BUG that can take away all your items)
VigilanceFix - Minor visual bug fixed with a single weapon in the expansion
FtG UI Mod v2.1 - Fixed issues with the fonts being too small in modern HD

And the free DLC A Tale of Orzammar, a cannon DLC that is a prologue to the Dwarf Noble Origin (not big deal). http://dragonage.wikia.com/wiki/A_Tale_of_Orzammar For the first game, I think that alters the (gameplay) experience. DOG has power, therefore as an extra character has an impact on the challenge of the battles.

The game is very big so there's no need to lengthen it with additional mods.

Thanks for the help and info

Well, in the expansion is possible to do it.
In the first OC is not possible to do it. Yet, as long you focus on a single specialization for rogue and warrior, you are not wasting skills, and even then, is feasible to finish the OC. Once the expansion begins, you can re-scope your character.

For casters, as long you finish your line (the four spell in a single row), should be enough. The game will give you a healer and a "dark user". So, you can experiment a little more in any other row.