Just a thought - how about illustrating your actual network so that we can have a better view what makes sense and what not. At the moment it is a little foggy for me.

So, how many workstations do you need/have and how many render "slaves" do you want? In my eyes this is the first step - to define the needs for let's say the next two-three years. And then try to find out how to get there.

For the machines that are discussed here i would say it needs not many render slaves really to have a really powerful setup.

AND, you can always grow. If you need a Mac for video editing AND 3D (and i guess you do not want to repurchase especially the video software for a new Windows machine)  then go for a Mac Pro. Full stop, no alternative. Then, if you find out that you need more power for 3D Rendering you can add a powerful Windows machine to the toolbox, Vue for example comes with both versions, Mac AND PC so you will not need any extra investment on the software side.

I personally - and i am absolutely no network expert - found the networing of a mixed machine environment not very difficxult. Especially when you do not want much more than file exchange and backups. And i guess that is what you mostly want to do.

One day your ship comes in - but you're at the airport.