You can make the adjustable preview as big as you want it. The problem I have had is that once you build it in a certain size there is no way to automatically make it bigger or smaller and appropriately adjust the channel images to the new size. So create a new profile with some channels and then play with the adjustable preview window size until you get to the size you want to see. Note that size and make you real preview that size. If you are using a picture of your house be sure the picture of the house is big enough to show what you want, because the picture will not resize.
Once you figure out the size of window you want then adjust the pixel size up or down to get the fine control that you want. What I did for RGB last year was to use a small pixel size and define each color pixel adjacent to the other. You can also define the channels on top of each other, i.e, same pixel, and the colors kind of blend together. When I was using 3 colored strings around my windows I wanted to be able to tell when I had both two colors on because I like turning two colors on together. For instance. my non-rgb windows look good with blue and green lights on or red and white and I wanted to be able to see that difference in the preview and a blended color was not what I wanted.
Attached is my 2011 preview. I do not try to draw everything exact I only need a representation of things to let me see how things are going to be. The vertical bars are actually minitrees, the bottom right is my representation of my megatree and the 3d star in the middle of it. I the middle of the tree is rotating then the star is rotating, If only the red pixels are on then the tree is red. etc. Crude, but works for me.