No problems with lead free solder here, and thats using a boggo standard Antex soldering iron. It needs a little more time to heat, but other than that, it's all good.
But I admit, leaded solder is bit easier to work with, so I use that for repairs, and, umm, build 'errors'
As for ROHS, as Guest says, the rare components won't be ROHS as they are already 20+ years old anyway. But other than those.... It should be doable. My first x0xb0x build was self sourced.. And pretty much all the major suppliers show on their websites whether the selected parts are ROHS certified or not.
That said, I think the whole ROHS thing is complete bollocks anyway.