I talked to Jose about the local Overleaf server. You may ask them to activate your onsager account and then you can use it with no limits. The only thing is that it is independent from the general network of Overleaf, so you cannot add collaborators from outside. To collaborate with someone the only thing you can do is to generate a link with rights to modify and share it with your coworkers. 

It’s not optimal but it can work. 

Best, 

Dani.