I wouldn't say his 'number' (or lack thereof) is a red flag. But the way he talks about his past with you is really disrespectful and it sounds like he's either trying to brag about his conquests (eww) or somehow make you feel like he's better than you becuase he can get laid whenever he wants (also, eww).

There's a way to handle these conversations without being an asshole. On the bed thing, he sounds like he was just looking for a way to bring up that he's had sex with a lot of girls. Like you can have sex with a lot of people on a full size or queen size bed, same as a king, so I fail to see how that's even a proper response to your question.

On the dating thing - maybe don't ask this in the future. In most adult relationships, someone's 'number' doesn't really matter. Eventually you can bring up the serious relationships you had in the past because those (and the reasons they failed) can give you a lot of insight about a person, but the question of how many people someone has dated or slept with is mostly irrelevant