Yes, the more EE heals more and worth more.

Unfortunately, a lvl 1 charm wont sell for much, if any.

Goes in the right slot, stat charm on the left.

Depends on your playstyle, but heal charms typically will go in the accessory charm slot. EE will increase the amount of healing (or damage) of any charm whether placed in the main slot or acc slot. However, in the acc slot, all charms will only do 75% of healing/damage.