First of all, even if he does agree to see you out, do you want to spend your time with someone who is "not that into you?" This has never panned out in the long run for me. Yes, he may meet up with you, but it will not result in a LTR where he is gaga over you.
If we wound up just being friends, I would have no complaints. I tend to approach meeting someone new with as few expectations as possible. If I enjoy their company, I want to get to know them better (whether we ultimately wind up dating or not). That's part of the reason why I kept the email so low pressure.
The way I see it, emailing him has three potential results. He can (1) accept my offer, (2) make a counter-offer, or (3) explicitly reject my offer / ignore the email. I assume he will elect option (3), so I'm not going to give the matter another thought unless I hear back from him. However, it does give me peace of mind that I've clarified any mixed signals I may have accidentally sent while on our date.
As for the happy hour itself, I'll just plan on bringing a few friends and having a good time with them whether he shows up or not.