Been reading up on few stock maker books, and a common finish schedule was to use some sort of varnish to seal and fill the grain, then finish with several coats of BLO rubbed in.

Armor-all as in a car detailing product? Never heard of that and not sure that I would want to use a silicone based product on wood. I build custom furniture as a side gig and use a lot of different finishes. Always tell the customers not to use silicone products on the furniture I build. Now back in the old Army days when we waxed and buffed the floors, a trick was to use armor-all with the last buffing pass to produce a higher, longer lasting shine, but that was on linoleum floors.