Get a some estimates and pick their brains on your townhouse pros, cons, pricing, etc.
All the best to you.
My understanding of a 2-stage furnace is that it has a low temp stage and a high temp stage. Most of the time it runs in the low temp stage and keeps the home a more even temperature. The high stage is used house if the heater has been off overnight or during the day when you are gone. We have anew 2-stage furnace and we really notice the difference from the old 1-stage furnace. Also, our gas usage dropped 30%. Our old heater was at least 25 years old. Be sure to talk with your heating professional for advise. They should be able to look at your home and recommend what is best for your needs. If you need the name of a good heating contractor, please contact me.