so, what kind of materials can i use that require no special hardening after turning/milling/cutting?
Prehard 4140 will suffice for a lot of parts you describe.
It's not too hard that you can't machine it even with HSS cutters.
Unless you have access to case hardening, I'd avoid 12L14. It's so soft it almost cuts like butter but after case hardening it becomes a marvelous material for non-stressed parts like followers.
I made "poly chokes" for Herters many years ago and the material used was "stressproof"...or IIRC 1144 steel....that was a long time ago....and IIRC they was not heat treated.