You have a variety of different window layouts.
I've elected to have my Taskbar visible on that monitor.
That might be the easiest for you.
The aspect ratio of the windows is still the same, and they're rendered the same even if the slaves are scaled down... so everything is still instant swaps, and mouse broadcasting is accurate.

I have a layout, where the four slaves each take up a quarter of my second monitor.
As in, no extra space.

I have another, where the four slaves in total occupy a quarter of that monitor (1/4 each, of the top 1/4 of the monitor).
Which leaves me space for my XSplit, iTunes, Firefox and Windows Media Player.

In both of these layouts, the main takes up the entirety of the main window, but with the Task Bar visible.