Shimano road shifter/caliper/hose compatibility

Looking to build a a road bike with some parts I have lying around. The bits are..

rs785 shifters

Bh59 hose with a banjo on one end

1 grx caliper

my questions are.. I think the hose is correct but if not will it still work? But the caliper I’m sure requires bh90, as do all the newer flat mount models from shimano which I’ll need to buy one

will any shimano caliper work with an r785 lever and any hose?

They’ll fit together fine. Shimano recommended BH59 hose on early non-series road brakes for feel reasons rather than anything else – BH59 is less resistant to expansion than BH90, and so should give a slightly softer feel, though bleed quality will potentially have a greater effect.

As long as all your fittings are correct for each end of each hose, it will be fine.

Cheers