I was the same. I wanted to make it last as long as I could. There was no way that I was going to rush through the story in 20 hours, and honestly, I was kinda surprised when I saw that some people on here finished in like 3 days after release.
I managed to get a PS4 copy on the 15th, so put 12 hours into that before switching over to PC (my main platform) on release day. I had to start from scratch, and it took me 72 hours on my first playthough. I talked to pretty much every character every single time that there was some kind of story progression. Because of this, I managed to do every request, apart from 1. I also got pretty much every move scroll in the game, and levelled them to max... That was a bit savage to be honest.
I was playing on PC on EGS, and sadly, that doesn't have achievements implemented yet. I would have unlocked most of them, and would have used NG+ to go back and finish them all. On the upside, it means going back to the PS4 version for my second playthrough will be a lot more fun, as I'll be able to hunt for all the trophies. I was going to start straight away, but decided to put a game in between instead as I don't want to get burnt out on Shenmue. Currently just started Death Stranding and will return for the Shenmue 3 trophy binge after that!