Boas normally won't hesitate to take f/t even if they've only had live before. Just make sure it's warm like you would do with a ball python. I highly suggest using feeding tongs.
A healthy adult boa is fine to eat one appropriate sized food item every 4-5 weeks. I judge based on girth, my boas that are 6' usually are on larges, but again it depends on their size.
Good luck with your new guy!