Possible to setup default settings?

I have a few questions regarding settings for the different sites.

As it is today, when I setup a new site for someone, I have to go into the theme settings and manually change a few things i changed on all sites that are not standard settings. Is there a way to make those settings default for every site? (such as link colour and stuff)

I am now thinking about letting people register to blogs whenever they like. As it is today im the only one who can setup and they have to apply to get a blog. If so, could i make default settings for the logobanner to always remain in all sites? (even if i let them upload their own as well..?)
Or could I maybe make a smaller logo in the left hand corner as default and then letting bloggers to choose their own header, if they like?

Thankful for help!