I understand this is more caused by USA stupid rules than what you want to do. But .1BTC for a card that stops working after less than 1 BTC is used is very expensive.
I have an anonymous Limited card and live in USA. is the $300 Limit maximum I can put on card or after using it to spend 300 it will no longer work?
I also have another old anonymous limited card I have not activated yet can I give/sell to someone else? (probably a raffle prize at a bitcoin meeting)
The limit tells you the maximum amount you can spend through the card before needing to raise limits (however, US residents cannot raise limits). If you can't/do not raise limits, the card will no longer work.
You're free to do anything you want with the other anonymous limited card that is in your possession (you can even add it to your balance once you reach your limit on your first card).