Hi there,
I'm interested in building a site that people come and pay to listed their sites on it.
Does Google penalize type of this site when it has too many outbound links on a webpage?
Like 40 to 70 links on each one?
Outbound links are not bad, at following cases:
Relevant link which adds more information for your visitors.
Relevant link which links to high quality sites.
But linking to low quality and banned site definitely hurts your ranking.
I've always followed the guidance of keeping it below 100 dofollow outbound links (nofollow not an issue)... and yes this can cause issues - just look at the way G has hammered directories out of existence with some evolving to be used for negative seo!
So I'm surprised that you are even contemplating this with setting up a directory in the first place and further I would be even more surprised if people where prepared to pay for the listing especially if you did not have massive traffic numbers to back up the ROI - which I'm sorry to say is highly unlikely given G's attitude to such sites in the first place...