I may not be the most qualified to answer all your questions, but I'll address then the best I can. I don't often pocket carry outside the house or yard, and, when I do, it's a glock 26. I do generally carry lots of stuff in my pockets etc..
Pocket knives: I carry two daily. I transitioned from right side tip down to Endura tip up right and Delica tip up left. I only use the Delica. It took some getting use to, but, like your pistol draw, you learn it fairly quickly. When I pocket carry, I put the Endura in my back right pocket.
Illumination: I also carry two lights regularly. A surefire backup rides right pocket above the knife. A 6P pro rides in a holster on my left hip in front of my spare mag for a 19. When I have to be more presentable and tuck in my shirt, the mag and light often get left off. No gun I'm that situation, I leave the light in my right pocket. Pocket carry, it goes to the left.
I prefer to have a spare mag, but occasionally have to go without due to clothing requirements.
In the truck, I usually put my 19 in an accessible place (door or between the seat and console). Drawing from my pocket in that situation is almost impossible, but I prefer to keep a gun on me in case I need to bail out. I don't want to risk not having one on me in that situation.
I hope I helped a little. I plan to get an LCP when finances allow.