No. No license is required.
A rail interface system or a mount on the top
Usually not. But you must cock it between each shot.
8.4v 1500 mAh
I don't think so but check just in case
In general, no, However, the requirement for ANY kind of license for ANYTHING depends on where you live- and you did not share that with us.
Air Soft guns. Yes
in general 180 $ is the minimum for a reliable rifle.
soft clean cloth
No they are not illegal.
Try oiling of the gearbox.
If you rifle is a slide action repeater (pump rifle) these DO have a collector's value. It will be based strongly on the condition of the rifle. It could vary from $250 up to $800 for VERY good condition. Strongly suggest you not attempt to "clean up" the rifle other than a wipedown with a soft oily cloth. You WOULD need a hands-on appraisal.
No you don't as long as the buyer is over 18 yrs old it is all legal and ok