SEO for a website which provides projects for freelancers

Hi guys,

I am currently in charge of a new website project where we try to connect freelancers to project owners and vice versa.

What we basically do is building an Upwork clone for a specific niche.

Since I never did SEO on such types of sites with all their specialties I need some help.

Main questions at the moment:

• how to handle expired projects?
• hundreds of pages with no obvious keyword focus such as the profile pages of the freelancers: how do I attack onpage SEO here?
• what would be a clever way to build a good site structure?
• how do sites like this work in terms of ranking goals? Should I aim for the homepage to rank for all the obvious keywords such as "find freelancer", various jobtitles, "xyz freelancer" or is there any need to build further category-like landingpages?

I woul be glad to here some ideas which point me into the riht direction!