I have a double immersion chiller I use for 10-30 gallon batches, I only use one with small batches, and use them both in big batches. Each has it's own in and outflow, I can chill 30 gallons to pitching temp in 15 minutes or so.
Double connected coil seems like a good idea if you have height constraints.
Prost!
Edit, you can see mine in my profile pics