Frankly I don’t think there is a ‘right’ number.
I’d post and keep an eye on how often GBot shows up to check it, the more it shows up, the more you post, so it shows the activity, but I think it can be overdone too.
Just my opinion, but I think it depends a bit too on your traffic, surfers, and content. Too many new posts will drive older one’s down, so if your traffic seems to peak at certain points, I’d add a post just before those peaks to give them new stuff, keeping in mind not everyone surfs every day or every hour.