Do you have artificial lighting? I love the idea of grasses in a pot indoors. I use ornamental grasses an awful lot...what kind of grasses would you be using? Not so much indoors because lighting is a constraint.
As far as a wood planter, any wood except for pressure treated (will DISSOLVE your screws, seriously I had no idea, you'd have to use powder coated hinges, screws). A really cool product would be Treks or similar. Dimensional lumber made from plastic bottles...looks like wood, cuts like wood, have to drill holes for the screws, can be curved with a little heat and will last forever. No need to line the interior. Comes in dove gray and that really looks like wood. Other colors as well but for planters keep the pot simple and understated so as to to compete for attention.
I wouldn't use Walnut either...
For use indoors all you need to do is LINE your planter with black construction 3 mil trash bag material. Make holes in the bottom of course. 1 to 1 1/2" in diameter and cut the plastic to secure to the rim of your holes. There should be no blockage with wrinkles to catch water. No rock or gravel at the bottom below the soil. Only use sterilized potting soil. Shallow is better than deep! Most roots of most plants are within the top 4-6" of soil. The excess is fine for plants that will send roots down deeper but grass is pretty shallow and I don't think you will be able to make a long term planting of grasses. The best grass would be fescue. fine fescue lawns It is shade tolerant and very fine. Another suggestion would be blue fescue, Elija Blue. Tidy clumps of blue blue grass. Very structural/architectural versus the green fine fescue. The third suggestion would be Hamelin Fountain Grass; 2-3' high.
The soil will not come out again past the first few waterings but covering the hole with panty hose before filling with potting soil would be a good idea for indoors.
Use linseed oil after sanding very finely.
You should consider grow lights to be able to have vigorous more of a long term perishable. Great fertilizer and for this I would definitely use an organic slow release fertilizer. Better for plants in limited light and comes with necessary bacteria and fungus plants need for health. Not too much because of the light factor. Specialized pruning, mowing for different grasses. For instance the 'evergreen' grasses such asevergreen ornamental grass don't do well with cutting back. Just saying get to know the grass you are considering and expect to change it out for another grass from time to time. Plant the old grass out in the garden in pockets of a 'rock' garden or give away.