The planche and lever are very advanced and only need work when the pushup, pullup and handstands are pretty easy stuff. I put a good planche progression below. Dont worry about levers until you can do L-sit pullups for reps and toes to bars.
Pistols are hard to get but once you get them they are awesome for leg strength. Start by doing pistol negative to roll where to do the negative portion of the pistol until you cant hold it, roll onto your back as fast as you can, roll forward again onto the same foot and use that momentum to finish the pistol. Also adding height to your heel makes a pistol easier so try that. L-sits are easy to progress, just use some books or whatever on either side of your body for your hands, chair arms work to, tuck your knees in and lift your body up. Work on not letting your lower back/butt sag behind your elbow, once you get that just slowly straighten your legs, or just straighten one leg. Knees to elbows and leg lifts help a lot with L sit strength.
Let me know if you got other questions. This stuff interests me a lot.