Everything went fine, but you need patience!
The trackpad was jumping and selecting automatically what was displayed on the screen. Also from time to time it used to click by itself ... very annoying.
It was the third time I did. First time, I did it easily taking lot of time but the trackpad I bought was not running fine (the keyboard was not fully working, only part of it was working). For the precision, this first one I did not bought through ifixit. Second time, I decided to place the old origin unit back ...
Then I keep working like that for another 6 months. Then I decided it was not possible to work like this and bought a trackpad from ifixit ... double the price of the first unit. This time it worked!!!
The more you play with all these screws, the more they got "tired" ... the third time I wanted to open it, some screws were so "tired" that it was not possible to unscrew them with the P5 tool bought at ifixit.net. I finally went successful by using another tool provided also by ifixit but it was a little bigger so that I was able to unscrew the "tired" screw. Another tip is to scotch every screw on a piece of paper as you go through the steps, so that you dont loose these screws.