Getting Started with Multisite and Domain Mapping


I am just beginning to venture into multisite and the WPMU domain mapping plugin. I have installed both at our client site. I have little experience with either. I am wondering how we can set it up, so that:
1) A group of volunteers can be granted access to all sites in the network, but not the network itself
2) Can be able to post in the blog of all subsites, but not make changes to plugins, settings, themes, etc.

Please advise at your earliest opportunity. I have looked at the manuals for Domain Mapping and ProSites but was confused. I have not yet installed ProSites, but we want to in the future to give the ability for new users to signup and create their own subsites.