I can offer a suggestion. Be careful if you decide to go with a tankless demand heater. Most of them I've seen have an ultra fine mesh screen in the inlet of the heater. This is needed because there are tiny passages in the heat exchanger that the water has to pass through. If you are using this with reclaim water, you might need an additional filter to keep from plugging the screen filter. Just something to think about.
I replaced a 350K Jarco with a 200K BTU Takagi Demand heater for my floor heat. Its a 10 gpm heater. After I installed it, the most I could get out of it was 2.5gpm until I figured out the filter was clogged. I had to run an external 5 micron filter on it for several Hours to get all t he sediment out of the glycol. After I did that it ran fine the rest of the winter.
There are several Ultra High Efficient (96%) tank style water heaters available now. Polaris, AO Smith, American Water Heater to name a few.....This might be the better route for you since some of them boast 400-500gph 1st hr recovery rate on 200K btu...