I'm replying line by line not because my style is better, just different, and different ideas for OP.
I never play with power armor. Even on my survival playthrough I didn't touch it. I only play survival mode now and almost never use PA, but I keep decent suits in my "major" settlements, usually sanctuary, red rocket and abernathy.
1) Get strong back and the lone survivor for carry bonuses I use Codsworth or other companions and sometimes the C.A.R.T. mod. Prefer to use the points on traits or scrapper and gun nut.
2) Do diamond city blues for ultra-much chems Yes, but with higher charisma, the gold bars, chems, cig cartons and other goodies, I aim to buy the Overseers Guardian at level 2-3 before even reaching DC.
3) get addiction immune perk and 100%+ chem duration I don't use chems enough personally to justify this. I always carry one does of addictol in case and it's usually not far to a doc.
4) Build water purifier early for clean water Vault-Tec drinking fountains provide clean water, minimal resource cost, and do not get wrecked in attacks.
5) go stealth build + pistols + rifleman Sniper rifle also helps the stealth / non-PA style
6) Unlock ballistic weave early
7) buy overseer guardian early by selling the useless chems from diamond city blues like mentants and buffout (I only use psychojet and medx) Those are the two best drugs, psychojet in particular is worth shortcutting. Just dont hit by mistake!
Mob enemies: Deliverer
Strong enemies: Stealth sniping + stealth shotgun
Super strong enemies or when in a very hard fight: pop psychojet, kill everything
Yeah, Psychojet + Fatman can one-shot Kellogg at super low levels.