See the achievement list, on the PC version of Dragon Age two, purchased through Steam

They are stored in your Games for Windows Live account. So whatever account you made for that is what you'd have to log in to for your achievement viewing. Typically there is a Games for Windows Live front end stored in your start menu that you can log into to see the achievements.

Or just, when in-game, hit the Home key to bring up the in-game version and go from there.

At first, the credits available to you in the single player campaign is limited to that from missions alone. However, once you've fully maxed out either the zerg or protoss research trees, you gain the ability to trade any future research points into 10k worth of credits.

There have been mentions of a glitch with the way the game handles this: if you replay a mission you've already beaten and acquire protoss / zerg research points within that mission, it is possible to get the Moebius foundation to "purchase research samples" from you, even though you failed to increase your net points (you already got them once). In this way, you can accrue as many credits as you need, and can buy all the armory upgrades in a single playthrough.

Update: This method has since been patched.

As of now, the best way to earn the armory achievements is to play the campaign multiple times, selecting different upgrades on each playthrough, as achievements are shared across all campaigns.