Thanks! Missing your attacks may mean you're simply too far away upon pressing the attack button, or it could be a bug. If you could make a video recording, I could look into it.
Also, attacking without targeting the enemy can be difficult but still possible. If you want to concentrate on one enemy though, it's better to target them.
You could also try the top-view camera if you're having a hard time judging distances (press C to switch camera styles).
Stamina management is a big part of combat, so don't go crazy attacking too much since it will deplete your stamina quickly. Stamina is there to prevent any character from just attacking indefinitely (i.e. infinite combo).
Lag after dashing is intended. But to eliminate the lag, you can cancel the recovery part of the dash into an attack (provided you have enough stamina) if you time the attack button press properly. You can also chain multiple dashes together if you time the button press right.
I may increase his max stamina though, to compensate for all the new attacks I gave him. I'll see how it goes.