Great project and build you have going. Good call with going with a couple of Ultimas. Have heard nothing but great reports from all Ultima users I've questioned. I'm going with Ultimas for biological filtration instead of a traditional wet/dry filter.
If you ever decide that you ABSOLUTELY need more space, I have a very radical suggestion.......you could switch to a tankless water heater.....sorry they're on my mind as we just had one installed. Couldn't help but notice that big water heater right next to your tank.