dinged 100 yesterday and im completely lost on what to do. my end goal is to raid, do i just grind 5mans until im geared enough for heroics? or better yet, what CAN i do at 100?
In my opinion, at 100:
Do what you can for your garrison, if you can't immediately upgrade to lvl 3 then save resources for that.
Finish the quests in Nagrand. Not only are the cutscenes awesome but assuming you have a Dwarven Bunker the quest upgrades will be a huge help towards your iLvL for heroics.
If your low on resources, Nagrand has a pretty dense collection of treasures that give them. Download an addon called Handy Notes and the Draenor extension to see where all the treasures are and what they give.
Continue to manage followers and work orders. Followers, once leveled enough, start getting missions that offer real gear for you aswell as money and legendary quest items, they shouldn't be ignored. As for work orders, the only money to be made in this expansion will be items gated by cooldowns. Materials are going to be dirt cheap so farming I think will be a waste of time. Keeping work orders ticking is the main way to make money.
A note on that: The most important one could be the Barn work orders. At level 3 the Barn provides Savage Blood which is required for every craftable upgrade in the game. Not only that, but the level 3 Barn takes quite awhile to unlock, something like 24 days if your only using one character. Savage Blood is going to be the main bottleneck for craftable epics by a pretty large margin, unless there ends up being a way to reliably farm alot of Primal Spirits. Right now I'd advise everyone to start ticking Barn work orders as soon as they can.
Do the daily and kill the rarespawns there. Most drop iLvL 620 loot.
Eventually at 610 once you can do Heroics, spam spam spam. Loot has alot of variance in terms of quality now with warforged being able to be on everything and random sockets. Edit: Oh and of course do your Legendary quest ASAP.
At 625-630 you can start doing Challenge modes. There's a daily that gives a guaranteed 640 epic every day for just completing a challenge mode. You don't have to medal. Some are harder than others. In my experience so far Skyreach is worst, followed by Everbloom. The others I've done aren't so hard really. They all require coordination though and you should expect to wipe on the hard fights with a pug until people really iron out the pug strats.
Another venue for gear past heroic dungeons is Apexis. The fastest way to get these once you've done your daily is to joina Pit farming group in Gorgrond. With a decent raid and a good route you can get 1-1.2k Apexis and hour this way. It is fucking mind numbing though.
Finally if you have some gold in your pocket, start shopping around for good craftables. If you value crit as a dps, the darkmoon cards are very very good. As a healer the darkmoon card is also very good. I dunno how great they are for someone who doesn't like crit, but the tanking one does have bonus armor which I believe is the best stat for most tanks where they can get it.
In December the raids come out and I don't think it'll be hard to get a spot if you spent this month gearing up diligently. Normal and Heroic difficulty look to be not so bad. Mythic guilds will of course be more selective than just gear.