What are my options for attaching my radiant tubes to spancrete main floor? im aware of the mats (expensive) or wire mesh and zip ties, is there anything else?

Im pouring a 2"concrete topping, should i use any insulation between the  8"spancrete and topping (the basement is heated) or is the extra thermal mass beneficial?

Heating source: Ive had quite a bit of experience with combination boilers in the UK but that was 10+ years ago (modulating instantaneous DHW with closed loop heating) Dont know whats available here/now but im aware of the real world efficiencies due to short demand cycling, some models we used had an internal DHW buffer tank for short draw/quicker response. So im looking for advice on heating/dhw source. Eventually i will be installing a geo heat pump but need to get through the next year at least.  Its a new house 1700sf x 2 levels plus a 400sf garage all ICF.

Any advice greatly appreciated.

Thanks