For AutoX, running the harnesses to the rear will be fine. You WILL NOT be allowed out on a track (except for Dunnville, because well, it’s Dunnville ;)) with harnesses without a harness bar and proper routing on a seat built for harnesses. New rules are going into effect for a lot of people who hold DE’s either this year or next (SCCA, PCA, BMWCCA, NASA, etc) which bans harnesses on stock seats in virtually any car.
AutoX harnesses, 4 point is fine.
If you’re planning on doing track duty, get the 5 point (or 6) with a cam lock.