Getting a membership and / or AC's?

Make sure you get Infinity Titan to start off.  It's identical to Stonecrusher, and one of the best classes you can start off with.

Kill Binky in Doom Vault for the Cape of Awe.

Obtain Lightcaster at Level 80.

If you buy a 40k AC package for $99.95 and aren't planning on getting Nulgath items, or if you get three or more 40k AC packages and are planning on getting Nulgath items (I recommend you use your first 4 IDoAs, 2 Mythic and 2 bonus, on rare Nulgath farming pets if you do plan to farm Nulgath items), go ahead and use your IoDA on a Necrotic Sword of Doom as well.  The NSoD is the best sword in the game.  This is the IoDA version, which won't give you any badges (that's the farmed version), although it will serve you well for now until / unless you wish to farm for the farmed version.