Yes...
Being a convicted felon could affect the "insurability" of a person. In other words, it could change the insurance company's evaluation of the "likelihood" that the person will die (other factors, of course, would also be considered, such as health, family history, etc.). Lifestyle can affect insurability.
NO
Not legally.
No. A convicted felon is a convicted felon regardless of WHERE they go or live in the US. Note: Use caution if you're even thinking about it! The federal punishment for felon in possession of a firearm is a minimum of 15 years in federal prison.
A convicted felon may not purchase, possess, or have access to firearms ANYWHERE in the United States as per federal law.
No.....
YES
Provided you are not a convicted felon, you can buy long guns at 18 and hand guns at 21.
You need to consult with a lawyer familiar with firearms law.
This is not a forum in which to discuss or recommend specific insurers. However, a factor that you must consider is the offense of which your son was convicted. The underwriting guidelines of any particular insurer may, for example, preclude issuing a policy to a convicted felon. This is especially true if the felony involved insurance fraud. Contact a licensed local life insurance agent or broker for specifics.
Getting a mortgage loan will be the problem, not the purchase. If you pay cash, then there is no legal reason that will stop you.
A gun part is not a regulated item. However, the frame of a firearm, known as the receiver is legally a firearm. A convicted felon may not possess a firearm, nor may they possess ammunition.