Splitting House - HVAC, Plumbing, Waterheaters

[Trevor Hansen]

Hey all! I'm new here. Hopefully you have some input!

I'm making my basement a separate unit. I'm digging a basement walkout and removing the stairs from floor level to basement. I have built a new, small room upstairs for W/D and HVAC with plans to do a small furnace for each floor. I originally was talked out of a zone damper system. Then he suggested it today, now that everything has been torn wide open. 

I feel like having a small furnace on each level will be a little extra up front, but will be the safest option for tenants down the road. I plan on continuing to Airbnb the basement but getting full time tenants in the upstairs. Note that I might add onto the upstairs to make the kitchen bigger. 

Now- water heater: It's a small house. 2000 sq ft, half up, half down. 2 bathrooms, 2 kitchens, 2 washers, 1 dishwasher. The ease of installation and space savings of a %90+ tankless is very appealing. Venting would be a snap compared to relocating my current tank style. 

With a 199k BTU, I think it would be more than enough for this small house, even with 2 tenants/families. What are your experiences with the tankless style water heaters?

Thank you!