Is there any problems with selling my entire collection to someone all at once? 15 long guns and maybe 10 handguns. Also do I need an ISP approval number for each weapon or can they all be listed under one?

There is no issue with selling multiple firearms to an individual who can legally purchase and possess firearms in Illinois.

You should be good to go with one ISP Transaction Number - "430 ILCS 65/3(a-10) - Any person who is not a federally licensed firearm dealer and who desires to transfer or sell a firearm or firearms……"

Make certain you have a list of the firearms sold and the required information for a period of ten years after the sale.

Thank You!!!

How to sell a gun in Illinois: https://www.gunrights4illinois.com/blog/how-to-sell-a-gun-in-illinois/