I had to replace the battery since mine was not charging anymore and I was NOT going to pay Apple's $500 amount. They were charging me that much for the battery replacement and trackpad cleaning. I came back home purchased the 64 bit driver kit, spudger and tweezers. In total I spent about $100 including the battery.
After watching videos on YouTube and following the iFixit guidelines, I managed to get it all done in one go. The trickiest part was probably getting the track pad out but with patience and a steady hand everything turned out PERFECT.
It’s all simple, just think of it as a puzzle using a few tools and the puzzle pieces actually do something so be gentle haha. Make sure you’re working in a well lit environment and/or use a sort of spotlight to brighten up those dim spots. Read carefully and take your time. I love how fast iFixit shipped my order and how quick it got to my place.