So I've been bouncing back and fourth between a few of these solutions. Some of which (such as page templates) I have used extensively, and I've recently started exploring shared install which seems to work fine. I gave multi site a try, but I didn't need my installs to be completely independent (needed to share the user table across all sites, plus some of my plugins just didn't work), so it wasn't really an option for me.
I have two questions in regards to child themes and page templates. The first, I've recently started using pre-built themes to cut down on development time instead of starting from blank and working my way up. I've noticed that sometimes, these themes come with their own plugin sets, post types, builders, etc. If I wanted to make a child theme derivative of these kind of themes, would it be a lot of trouble to work with? To explain what I'm trying to accomplish, I have a couple of clients that I want to format their specific sections using their own version of the template; each with their own unique changes specific to their site, ALL UNDER ONE INSTALL. With something like 2014, I don't see this being much of a problem with child themes, but with a theme with an existing plugin set where each individual sub site needs to have their own settings of it's included plugins, I'm not so sure...Then again, I could be wrong in how I'm interpreting "plugin". I essentially did not have to activate anything in the plugin section, but the theme does create dashboard specific sections upon activation of that theme.
The second question is in regards to page templates. When I started working with WP (not too long ago), my sub sites were pretty much page specific templates all grouped into one large theme (thankfully I can put this into their own folder). This was nice, however looking forward it does seem like it can get a bit messy as more sub sites begin to appear. I'd have to keep editing the functions.php to include those site specific functions, with a long if switch to check what page needs what version of functions, and I just realized that if there are plugins specific to that site, it could possibly bog the entire system down (might be why it's doing that now)...unless there's a better way of managing plugins that are activated on each site?
My question is would it be better just to create another shared install for EACH sub site that I create? In the long run would this still be a good idea if I end up with 100 or maybe 1000 sub sites under the same shared install? I already have a tool called InfiniteWP to manage plugin and theme updates across multiple installs so that part doesn't seem like much of a problem.
In any case, thanks everyone. Looking forward to some advice and suggestions in how to move forward with my sites redesign.