Re: suggestions before i build
Try not to build on a carpeted floor. Try to do it, in the kitchen or something. To get rid of static, ground yourself, by touching the metal chassis of the case for a minute. This will discharge any static electricity, from your body.
As for thermal compound, I believe I suggested you the Arctic Cooling Freezer 7 Pro, in that "Building A New PC" thread of your's. You don't have to worry. There is already a thermal pad on the heatsink.
Do not force any of the components, in order to install them. They only go in one way, so make sure you're putting them in correctly.
Before you turn on the computer, double or triple check, to make sure all the connections are tight and secure.
If you have any problems, you can always ask over here.
iMac 27" 5K Late 2014 | macOS 10.15.2 | i5-4690 @ 3.5GHz | 32GB DDR3-1600 | R9 M290X | 1TB HDD/128GB SSD