I don't think I'd go in or out, but just say "from now on".

I'd probably go with the "from now on" as well, but I'm certainly comfortable with "from here on in" through hearing it frequently and using it occasionally myself. Never "from here on out"!

I will admit, though, that the "on in" makes an awkward construction, and I wonder whence it came. "From here on in"to what or where? To me it implies that the rest of the journey (through time, through life?) is in the "inward" direction (towards home?) rather than "going out" into the unknown, into uncharted waters, which seems more applicable to life.