site wide plugins and setting up the multi domains

I have one site that has been running for a while with a lot of sub sites. (
i created two new niche sites ( and

QUESTION 1 - if i install a plugin on niche1 and network activate it it will activate for niche1,2, and 3 right? Is there a way to activate a plugin site wide? i.e all sites on get the plug but not niche1 or 3

QUESTION 2 - i created a sub site to niche2 and niche 3 ( and they work fine out of the box but i cant seem to find how to add a theme to and

another way to put it, if i go to nothing comes up - how do i add content to it