Staple ups require significantly higher water temps than slabs or above-the-stubfloor radiant systems (eg WarmBoard), or under-floor radiant using heavy extrusions (not bent/stamped sheet metal) as the heat exchanger between the tubing & subfloor.
First things first- count on AIR SEALING, then INSULATING the place, including the foundation walls (and put at least R15 under the new slab, if you jackhammer out the floor), and do a Manual-J type heat loss calculation of what the design condition heat load of building will be after the insulation project is done. That will determine how much burner and what type of radiation you'd need to run it all at a single temp that's low enough to be handled by a water heater. It's possible that a suspended-tube or simple staple up would require higher water temps than the operational rating temp PEX, but with extrusions it's likely that you'd still make it with 130F water, with at least some condensing-efficiency out of the water heater or boiler.
You might consider going with a radiant ceiling in the basement rather than a slab to simplify things, since that would be more responsive and likely closer in temperature requirements to the first-floor radiant floor than a slab would be, and more efficient, easier to implement, and less risky than radiant walls. (Hanging a picture in the wrong spot on a radiant wall can be a real disaster when the heating system leaks.)
Even as a DIY project it's best to find a competent hydronic designer for the heating system (no quickie web-based radiant supplier need apply.) You'll save more on hardware and fuel by paying for a good design than you'd save by skipping that step. If you can get the temp requirements low enough, a condensing tank type HW heater (Vertex or Polaris) would be a better choice than a modulating tankless, since it's inherently self-buffered and won't short cycle if you decide to break it up into several smaller zones even with low-mass radiation like staple-ups.