Figured I’d chime in here.
I come from a traditional background (various forms of kung fu) as well as a “modern” one (boxing & san shou kickboxing - compete in American & Thai kickboxing as well).
It’s the traditional martial arts that’ll tell you not to punch with gloves or wraps. The reason for this is to be more effective “in the street” so you don’t hurt your wrist or break a bone when you punch.
The Japanese method (various styles of karate) for achieving this kind of conditioning involves hitting hard things with a lot of force and no support.
The Chinese method (ie kung fu) involves hitting sand bags repeatedly, softly at first but building up intensity over a long period of time.
The modern philosophy (boxing, kickboxing, etc) is that wraps protect the wrist and the gloves themselves reduce the repeated blunt force damage on everything else.
It’s boxers who are infamous for punching harder than their bones & joints are used to because the gloves & wraps take those things out of the equation.
For pure explosive punching power, best to use gloves and wraps.
Stick with heavier gloves for sparring & shadowboxing; lighter (bag) gloves for heavy bag and pad work.
As far as a bag goes stay away from canvas & free standing water bags. Stick with the old fashioned leather or synthetic leather hanging bags. I’ve only seen martial artists use the water or gel filled bags, not sport fighters. A 100 pound bag should be fine for what you’re using it for.
For the Thai knee, it’s important to remember it’s not just the leg moving to raise the knee (like a sobriety test); instead it’s the whole body (almost like a hurdler). Both anterior and posterior core muscles are very important. Real power comes from putting your hip in it as well as driving off your bottom foot.
Some good exercises for the thai knee would probably be deadlift, hanging & weighted leg raises/knee lifts, squat, and probably kneeling cable crunches.