Yes. If it's an assembled rifle lower, you treat it the same as any other private sale of a rifle. If it's a stripped receiver, it's an assembled pistol receiver (or was sold to you as such), or it's an assembled receiver minus the buttstock assembly, you need to act in accordance with the laws of your state for selling a handgun.
Average is around $350. If you are looking for a stripped lower receiver, the price should hang around $100.
Yes, it will, but then it would be in an SBR (short-barreled rifle) configuration, and would be a violation of federal law if the lower receiver is unregistered.
Into the left side of the receiver.
yes
You need the services of a CNC machinist.
All M16s are AR-15s, but not all AR-15s are M16s. Most parts are interchangeable; however, the inside of an M16 lower receiver is milled differently to accommodate the auto sear.
Depends on the rifle- some do not HAVE a bolt catch. On the AR15 family of rifles, it is the left side of the receiver.
Licence requirements are based on the laws WHERE YOU ARE. They vary greatly from one country to another, and one US State to another. And YOU did not tell us where your are. In most of the US, no, a license is not required to purchase a semi-auto AR15. Your spelling of 'licence" may indicate you are not in the US. In Australia, a licence is required to obtain ANY firearm. An AR15 is a Class D firearm, and cannot be owned by the average private citizen.
Anyone can buy the M16 small parts - but it is illegal to use them to create a fully automatic weapon without the correct NFA paperwork. Adding these parts to a semi-automatic AR15 will not make it fully automatic, and some parts will not fit the semi-automatic lower receiver at all.
The AR-15 platform that can accept AK-47 magazines is typically referred to as the AR-47. This hybrid rifle combines the AR-15 upper receiver with a modified lower receiver to accommodate AK-47 magazines. This allows users to take advantage of the reliability and affordability of AK-47 magazines in their AR-15 platform.
Yours is a very broad question, and we will need some additional information to give you an answer with any meaning. If you mean starting from a bare reciever, that is one set of answers. If you mean atttaching it to the lower, that is another. If you mean assembling it with the BCG and operating handle, that is another.
A mid-length upper receiver uses a mid-length gas system. The barrel length is between 14.5 inches and 18 inches, and the handguards are slightly longer to accommodate the gas system.