Thank you wa8yxm, that's a good bit of the info I was looking for!
As well as DrewE, thank you!
Due to where I live, for 9 months or more out of the year, I'm looking at needing a 30 to *possibly* 40 degree rise in temp from inflow, and depending upon how creative I get, possibly less.
I'm also researching severely low-flow faucets and shower heads, along the lines of a gallon per minute, or less.
When I had it hooked up at the farm (recently sold said farm, and will have it hooked up at new, bare property while I build), water was a simple garden hose connection... And half the time the cold water side would scald you. I live in the blazing heat... consider input temps to be 70-75 most of the time.
Which is the only reason why I'm even considering this option. I can do a little creative plumbing and let Mother Nature give me a 20* rise before it even hits a tankless.