I'm a fan of natural finishes so for my previous book case project I made a wiping varnish from 1/3 mineral spirits, BLO, and Poly. I think the finish turned out great but had a couple questions.

The problem comes when I try to build up layers. It took 6 coats to get a good even sheen on the plywood/hardwood of the bookcase. Possibly due to soak in. I know multiple thin coats are better than fewer thick coats but I wondered if anyone had a take on or had tried the following:

For my son's solid maple toy box I was thinking of wiping on 1-2 coats of BLO then because its already likely absorbed its limit of BLO, I would wipe on a 1/2 mineral spirits/poly blend to build up a protective layer. Thoughts?

Also, do I finish the inside of the toy box? Any problem with using BLO or Poly on the inside?