It's a can of worms with no definitive answers, not least because, apart from a few ancient zircons, almost all the evidence has been obliterated by later processes.
Critical factors would have been the rate of crustal recycling, the rate and distribution of heat from radioactive decay, the extent and intensity of the greenhouse effect, the onset of plate tectonics, ratyes of magmatic differentiation, and the role of water in the early crust. Develop a model with your own set of assumptions - it's as likely to be as accurate as any of the multitude of models already existing.
The Hadean in total lasted about as long as the Phanerozoic, and even the early Hadean would have been not less than 100 M.a. in duration, over which time conditions changed massively.
Some temperature estimates for the Hadean include:
- Early Primitive mantle, about 1650 to 1850 deg C
- Mafic zircons 750 to 850 deg C
- Late Hadean zircons from Jack Hills, West Australia, 700 deg C
- Crustal rocks with plate tectonic under-thrusting, 600 deg C.
So my best guess for the early Hadean surface: Not far short of 2000 deg C.