Do I need to sign "me" after signing "help me"?
No, you do not need to add a separate sign for "me." Because "help" is a directional verb, moving the sign toward your body already includes the meaning of "me." Adding a separate point to yourself is redundant.
What if I want to say "I help you"?
To sign "I help you," you use the exact same handshapes, but you change the direction of the movement. Instead of pulling the hands toward your chest, you push them outward toward the person you are offering to help.
Does it matter which hand is on top?
Yes, your dominant hand (the hand you write with) should be the one making the "thumbs up" shape on top. Your non-dominant hand acts as the flat, supportive base underneath.