As for me personally I think I will start the game out as playing "myself" with my own name, make the choices I personally would do etc. And experiment and exploring a whole lot since it will be my first time of course. Experiment with the game and its systems and what is possible etc. I will most likely play as Dead is Dead though. I really love the feeling of danger, but just putting up the difficulty slider have always feelt so bad in previous Fallout games (and Elder Scolls games) since that only make everyone a bullet sponge, making combat feel very artificial and unreal when people can take 10 shotgun blasts to the head before dying.
After I die or grow tired I will probably try out a more specialised character when I have learned the games limitations a bit more, and go out in a totally different direction from last time to experience something new.
I think I will stick to DiD, but I like to keep some memento of a character and I really like the building feature so I think when he dies I will just retire him as a "ghost" at his house I have built. I can go around and look at what I managed to gather or do that playthrough but I can only stay around my house like he is bound there now.
As for other self inflicted rules I will probably also try to eat, drink and sleep etc even if there is no "hardcoe" mode.
Also I tend to not use fast travel if there is no logical way (like the carriers in Skyrim) or use the wait function.
At some point I will maybe also make a "complete 100%" character (not DiD obviously)
Or I will see, I don't know if I want to "100%" it because then some of the mystery might be gone when you never know you will see something new every time. I will at least take notes of bubble heads etc to be able to collect things like that later again since my DiD characters will probably not be around to ever complete a set even if I wanted to.. . I don't even know if 100% is even possible since there is no % in the game like in some other games, and some actions tend to shut off other.