I am curious, in training to increase my explosiveness (sprinting, vertical jumping, etc.) would it be regressive to incorporate gymnast bodyweight exercises such as planche holds, and front lever holds, as well as things like RX squats (static leg holds in different positions), seeing that these types of exercises are meant more for absolute strength and muscular endurance. While I'm not able to do a full planche or front lever yet, I am getting very close, but I'm still not sure whether or not these exercises are helping or hurting my goal of increasing my sprinting and jumping ability. In addition, are there any diet tips out there for getting big, but at the same time remainng limber and quick. Thanks.
Working on the planche and front lever holds will have no negative effect on speed/vertical jump height. They will probably help your overall speed slightly because of the added strength in your upperbody but will in no way hinder your lowerbody explosiveness. You could try adding some lowerbody plyometric exercises though instead of the static leg holds you said you were doing. Coach Sommers has an interview on here where he mentions some of the lowerbody training he does with his gymnasts, you might want to search for that.
The only diet tip would be don't eat alot of extra/empty calories so you dont gain any un-wanted fat, as that would make you slower.