Do I have to get half-life 1, blue shift AND opposing force for WON to work? im not gonna play blue shift nor opposing force just the classic one, so can I just buy that on its own?

you only need the steam version of the game you want to run for the WON, so yes you only need the original HL and not OP4 and Blue Shift unless you want to run those aswell but thats up to you :3

azorokazu ok thx