The only thing with walnut, or any tumbling for that matter, is getting it out of very tiny spots. Phillips screw heads being the most annoying in my opinion. Bearing in mind how many screws you end up with - I would just replace these outright.
Otherwise for tubes and such (hex posts) you may sometimes need to drill the media out with a 1 or 2mm bit.
This 100%. I used walnut and corn in the past in my tumbler. Corn turns nylon nuts a shade of green, and walnut turns it a shade of brown. Don't bother polishing anything that has nylon in it.
If you decide to go the tumbler route then get yourself a good pick set as you'll be picking the fine media out of every nook and cranny.
I don't bother using my tumbler any more. I just replace the screws and lock nuts. For standoffs, I'll replace them if they are really really bad, otherwise I just use some elbow grease and some 600/800 automotive sandpaper. For larger parts, like coil holders I'll use a brass wheel. Use an old one to clean off any heavy stuff, then switch to a new one to give it a good shine.
Afterwards, if you still have energy left, take a polish wheel to it. I just use a Dremel with a polishing pad and some red compound. You can use the green compound too afterwards if you want. I don't bother because I don't have any and I'm too lazy to go buy it. Lastly, I put on a light coat of wax. This is to deter any new rust or corrosion, but I mainly do it because the carnuba wax smells like the gum you use to get in packs of baseball cards. The carnuba wax masks the smell of old beer and cigarettes trapped in the cabinet of the pin.
I use XXX from the guys at Hardcore as my go to.
