Front levers and handstands are useful and included in the SFB material.
I would personally say that ab wheel is probably more useful in general than dragon flag, as it involves piking and is not merely a static hold (but involves something of an extended static as well).
A 'muscle-out' is holding a weight straight out in front of you or to your side with one hand, like a crucifix hold. It is sometimes used in strongman competitions. I assume you mean muscleups... I was able to do them without kipping and without specific training once I got strong enough, so I don't believe they should be prioritized.
Strive to simplify, not to include more 'stuff'. Push, squat, pull, hinge, do a heavy ab move, and go home. If you are interested in gymnastics, add a straight-arm movement and some skill work (handbalancing, probably, at first) to that; but no more.