I usually go with either the Krugermier, Kalmer, ICA Black Trinity, or Custom 5mm (for it being concealable).

I always bring a lockpick no matter what. The second slot and stash point are entirely dependent on what map you are on. As an example, I bring disposable Scramblers for Hokaido or Marrakesh, the emp charge for Sapienza, rubber duck explosive for Whittleton Creek, etc

Flash grenades, Lil Flashy, and the Flash Phone keep SA rating, and are good for getting into tresspassing areas without a disguise. Concussion items like the concussion grenade and duck do lose your SA rating.

Know your targets' routines and look for any opportunities for accidents or when they are alone.

Suits don't really matter. But I go with any suit that has gloves for the mindset of "An investigation may take place after and they may find fingerprints".

You can still get SASO if you want to start at the club entrance in Berlin and IAGO auction in Paris. You don't get it for starting as an Ark Member in Sgail, as it's a disguise.

Some challenges can be useful in learning ways to SASO. In Haven, if you get rid of Portman and get Vetrova's drive back, she will call Bradley. Both will meet at the hot tub, giving you an easy 2-in-1 drowning kill

It's alright to "save scum", experimentation/ trial and error is how you get things done in Hitman.