Acrylic wash over Tamiya?

The myth is that you supposedly can't apply an acrylic wash directly to acrylic paint. This is bull. Ask a figure painter, they do it all the time, at least with water-based acrylics anyway. If you apply a wash with an acrylic that has solvents in it, you may get into trouble. Always test first. Vallejo's washes are water-based, so you will be fine applying over anything.

I personally don't buy the "Tamiya acrylics are lacquers" rumors, but that's a discussion for another thread.

Tamiya acrylics are lacquer-based, believe it or not, and are extremely tough. You don't need any clear coat at all. Putting Future on it will ruin the effect because Future is self-leveling, and so will fill in the grain of the wood. Nope, just put it over the paint. Make sure you use a tiny dot of some kind of soap in the wash to help it flow nicely.