To be honest, I don't think acrylics will work over future. I strongly suspect it is water-based as well. Thus, the solvents might damage your future coat. I also work with acrylics mostly. What I do, is to spray a clear enamel or Tamiya's clear spray (X13, I think). That does not get affected.
The wash: you made the thin wash. Now just take a brush and you can either brush it on where you want it, or let it syphon into panel lines by just dropping in a little. Either way, you end up with a rank mess. I then wipe a cloth/earbud with a little bit of thinning agent (for acrylics that's either Tamiya acrylic thinners, Windex, or whatever your preference is) over this "mess". You should end up with a cleaned up model, with your recessed darkened.
Best is - try on a scratch piece to get what you're comfortable with.
Good luck & enjoy!