Don't order parts from eBay
Water damage doesn't mess around. My wife left a glass of water on the coffee table, which I bumped when I stepped over the dog. Battery, MagSafe plug, and logic board all corroded.
So, I didn't think the logic board was toast and just replaced the MagSafe and batter first, but then the darned thing wouldn't boot. At the time, the logic board was $500 from iFixit, so I got greedy and ordered it from a seller on eBay. That was a bad choice. The logic board they sold me was defective and they refused to refund me the $300 that I spent on it. I chalked it up to experience and sat on a busted computer for a few months. Finally, we budgeted for it, and the price of the board dropped a smidge and I got the parts in. They shipped faster than expected, and I got to work. The guide is a great resource for doing things in the right order. I had it done in 45 minutes, including cleaning the thermal paste from the heat sink. The computer works wonderfully now, and I can touch it without it crashing now. Huzzah!!
The thermal paste method is the center smear method. Just put a small dab on the chip and smear it over the whole thing. You don't need much at all. Be conserve with it.
Also, you don't have to wait until the end to take out the RAM. Do that whenever.
Also also, make sure all the connectors are in solid before buttoning it back up. Better to only open the case up once.