Congratz on the Acoustic. that is awesome. I am keeping my eye out for one, but am not looking to spend that much, but when I find the right deal, I am getting one for sure.
As far as the thumb rest. I can’t answer that, but I would say that if you were to add one, which is PROBABLY OK to do, that I would think about finding one, or making one yuu can glue on, instead of trying to screw thru the thin wall of the face of the bass.
But if you do want to bolt it on, you probably will need to drill small holes, and then get some bolts with two smal nuts so you can use the nut and a washer to hold the bolt, and not rely on the small wall of the face of the bass to hold wood screws in place. i would think that over time, you would rip some wood screws out, and possibly damage the bass.
You might get somethig for a thumb rest, and use some double sided tape to fix it in place, and then you can move it around until you find the right spot. Just don’t leave, or the tape on for too long so you don’t have to scrape it off.
About floating thumb, it is always a good idea to use this method for muting and strong right hand technique, so this is not a bad idea for your A D and G strings.
If you can learn to just anchor your thum DOWN on the bass, then you may not need a thumb rest at all.
When I started playing sting rays, with out a neck pick up, it felt a little strange at first, but I got used to it and would not want or need a thumb rest for ithem.