As for games the only ones i have purchased so far which was late last night are Battlefield 4 plus premium membership, WoW, and i Pre-ordered Battlefield Hardline plus premium membership.
One thing to try to keep an eye on are sales. It can be a little more daunting than on a console, because there are so many places to buy PC games. Consoles have only recently opened up to having other stores sell digital copies. Anyway, if you install the Enhanced Steam add-on and browse Steam (in the same browser), it will tell you the current cheapest price for a game and the historic low. It's also good to check out the latest Humble Bundle. As of writing, there isn't going to be one until next Tuesday (3/17) as the weekly one ended a few hours ago.
Green Man Gaming also has some good deals with their VIP section. They've got a few AAA games for about 20%+ off such as Batman: Arkham Knight and Mortal Kombat X. I purchased Cities: Skylines (just released this past Tuesday) for about $10 off, and it's only a $30 game!
EDIT:
Computers are my main Hobby now so i"m definitely looking forward to learning everything i can including how to build custom water cooled rigs.
I can tell you that water cooling is certainly a good way to spend a lot of money.

Costs really add up if you start buying premium components. A water block for your CPU will run around $70, the GPU is around $115 (+$25 backplate). A good radiator can run you between $40-120 depending on potency and size. Surprisingly, pumps are pricey. A single D5 pump costs around $85+, and it's not uncommon to use two for redundancy.