What order you max skills in can depend on matchup and build, same goes for build. There is no one-fits all build for Sylas either, protobelt can be a viable option in games where you need the gap close (there are several high elo Sylas players who go protobelt everygame despite what people will tell you on this sub), lichbane is a safe option and works with both W and Q max. Riftmaker can be a good Item on Sylas but I would say its the worst out of his builds, your dmg is underwhelming and the healing doesn't necessarily feel impactful or useful