Here's the recommended stats:
Recommended Specifications
CPU: Intel Core 2 Quad 2.4Ghz Processor or equivalent
RAM: 4 GB (Vista) or 2 GB (XP)
Video: ATI 3850 512 MB or greater -or- NVIDIA 8800GTS 512 MB or greater
DVD ROM (Physical copy)
20 GB HD space
You'll probably want Windows 7 or 8
As for mods,
Lady Karrakaz has an excellent guide. (Link is to old forum)
My current game has the following mods running:
All the DLC from Bioware
Advanced Quickbar
tal's storage chest
the magic box (yes that's right I have two chests in camp. There's another at Soldier's Peak. Today on Hoarders...)
Lock Bash
Skip the Fade
The Phoenix Armory (best armor for women)
No helmet hack
Universal Dye Kit
FtG Quickbar
Dalish Mage Mod
Natural Bodies
Add Any item Visual Deluxe (Very nice for spawning any bugged or missing items. Ancient Elven Armor pieces...)
CC Extra Tints and Tones
JB3 textures
Loose Stuff
More Hairstyles
Pineappletrees Vibrant Colors
Platinum Blonde
Proportions -dwarf -elf -human
tucked hair
Rockband
ZDF
I have Improved Atmosphere, but it and ZDF can interfere with each unless you are willing to put in more work than I am to reconcile the two. So, I generally use one or the other, but not both at the same time.
Hope that helps!