At least you didn't pick make an RTS as the game you wanted to ma.... oh wait, nevermind...
[quote:3a15sdd3]1. How to make a manual in-game click and drag selector (to highlight units)
Try making a sprite set to low opacity that is set to visible with mouse click and drag, have the sprite scale large with the drag event and then have an "is overlapping selectionSprite" in everything that can be selected.
[quote:3a15sdd3]2. How to make a manual character panel for each sprite
Not sure what you mean by this.
[quote:3a15sdd3]3. How to make multiplayer engine (Having a hell of a problem on this)
This is like going to NASA and asking "How do I get to Space?"
There are several tutorials and example .Capx on these forums for multiplayer but this will be your biggest hurdle.