Regarding assembly: even with carefully tucking the ribbon cables down the side while reassembling, it’s still hard to get that area to stick down.
I second this advice. I skipped it the first time, and the home button was too wiggly (although it worked). Now that I’ve replaced the screen a 2nd time (ugh), this time adding a new gasket, it’s a bit more firm, but still more wiggly than originally. If you don’t mind the button being lose, you probably can reuse the gasket, but if I have to do this again, I’ll probably get another gasket.
I had some difficulties, but was ultimately successful. The biggest problem I had was that the old glue strips didn’t want to come off, and snapped easily. Fortunately, I had an iOpener kit as well (for another project), and eventually was able to get the old battery out and scrape off the old glue.
I didn’t have too much of a problem keeping track of the screws, although a screw mat would help in this regard. The problem I had with the screws is that they are so tiny! Very hard to work with. I managed to lose one, which I have deemed non-essential.
Another problem I had is that the screen and digitizer cables are too short for the screen to prop up at a full 90 degrees. I managed to disconnect (or perhaps it wasn’t re-connected right in the first place) the digitizer cable, as when I turned the phone on, it had vertical lines through the screen. I unplugged the battery and re-seated the 3 cables that connect to the screen, ensuring that they snapped into place. A bit tricky to reassemble.