Can someone help explain user registration with MultiSite?

Hello all you MS experts,

I’m relatively new to the whole WordPress MultiSite world, but need to get up to speed and FAST. Have a big project running MS that is set to launch in late October.

Can someone please help me make sense of the user registration process with MS? With regular WordPress, a user registers at wp-login.php?action=register correct? (Correct me if I’m wrong…)

BUT with MS, a user is registered through wp-signup.php, yes?

I have done my fair share of digging and trying multiple plugins, etc. The issue I’m running into is I’m using the Make Your Site Social plugin, so I need to make sure that I can have signups via Gigya and a user’s social network as well.

My question is this:

Is there a way to take the signup form from wp-signup.php, and place it into the front end of my site? For instance in a modal?

From a UI perspective, I’d like to have the ability to register on any site in my network, but not take the user away from that specific site that he/she is on when they register.

Make sense?

Look forward to some responses!
Thanks all!

Alex