I am installing hardwood running into another room. Can I go into this room part way then continue laterally? The reason for not installing to the end of the run at this time is because the sink is not out yet but there is a lot of floor I could install if I could continue laterally at this time

Depends on the width of the doorway, and the plank width. You want to avoid showing a "stair step" pattern. Sometimes you can take a few rows out further into the room, and keep a random pattern going, ( I think that's an oxymoron "random pattern"), hopefully you know what I mean..

Do you mean you might have to go backwards in that area where the sink is not out yet? I say yes.