You should get a decent SSD now, it will definitely improve boot times and game load times. 128gb would be sufficient for the OS and a handful of games. If you already have a 1920x1080 monitor, no reason to upgrade any time soon. Closed water loops are highly over-rated, and as long as you have a decent aftermarket air cooler installed you'll be good for some moderate overclocking. Custom water loops are only for extreme overclocking builds. If you have a decent keyboard and precision mouse already, you won't have to upgrade until they break. Hell, you probably don't even need a precision mouse unless you play a lot of fps games. If you want headphones to mask out noise or because you don't have a decent speaker system, make sure you invest in some good ones.
Yeah, then I would definitely get a 1920x1080 one first, especially if you're gaming. Also make sure you have a good video card, if you don't you might want to upgrade (if you're just gaming on a 1920x1080 monitor, a 7870 will be just fine)