I don't know the answer...but to add to the fray...I'll throw out some points to consider.
How many KEGS fit into the available space?
How many taps can you get over a given size drip tray?
How much space do you need between taps to prevent decorative tap handles from getting in each others way?
And for Kegerator guys/gals... is the plastic shelf structure on the door in the way?
Here's a few places that I screwed up...
I can get 5 corny kegs in my kegerator...If I had THAT to do over again...I would have gotten a fridge wide enough to hold 6.
I started with 2 faucets...then went to 4. The spacing that I started with on the original 2...I tried to keep uniform when I added the other two. The spacing is grand for large tap handles...and it looks pretty good.
Then I found a drip tray. The four faucets fit over this drip tray perfectly.
Now....I'd really like to add a 5th faucet. If I keep the spacing...it will look off balance to add one to one side or the other. Five faucets won't fit over my drip tray. Hmmm.
So...if I had it just the way I wanted it... I would have started with the drip tray...and evenly spaced the number of faucets that the kegerator has room for over that real estate...and just checked first to make sure the tap handles don't interfere with each other.
I'm sure there are other considerations...but these are the ones that keep my mind busy.