You have the right idea going into it. I'm assuming you mean for it to work like an SRK(Shouryuken)? The velset you have is fine. Basically, having the char rise on the anim frame they're suppose to/you want them to. You have to change the statetype and physics of the move once your char is in the air though. Use a statetypeset script to change the char to air type(type=a) and most times people generally use no physics(physics=n). However, you don't have to use no physics, this is only if you want to fully control all the chars momentum, gravity, etc. once they're airbourne. If you want, you could just set the physics to air type (physics=a) and MUGEN will handle all that automatically based on your char's parameters. It's up to you how you want to go about that. Have the statetypeset script trigger on the same anim your char rises from the ground. So, in this case above, it would be AnimElem = 3. You anim should also loop or have an time of -1 for the last frame. Whichever is more befitting of said anim. This is so you char won't change anim in the air or repeat the entire anim over again.
Once you have that out of the way, you need to possibly create a landing state for the attack, or have you char go to their default landing state. MUGEN reads state 52 as the default land from jump state. So, you could do something like this...
[state #, Land from uppercut]
type = ChangeState
trigger1 = StateType = A
trigger1 = Vel Y > 0 && Pos Y >= 0
value = 52
The first trigger1 has MUGEN check if you char is air type. This is so your char won't change to the landing state prematurely. The 2nd trigger1 has MUGEN change your char's state once they reach ground level. You can create you own landing state. In which case, you'll have to change the value number to said state. Along with making sure to put a posset script inside said landing state, with a y value of 0. This is so you char won't sink into the floor. There's several ways you can modify this and so on, but this basis should be good to work with. MUGEN is all about trial and error, so don't feel discouraged if you get some thing wrong at first. Experiment and try different things. Eventually, you'll get the hang of it. I hope this helps.