I'm looking for suggestions for general purpose gunsmithing stones, something that can be used for a little metal removal, polishing etc. What size(s) and shape(s)? What material -- e.g. india, Arkansas, ceramic?
Medium and fine india are great options for moderate to light burr removal. For final polishing I like the fine white ceramic. Although if you happen to find anything in hard Arkansas those are amazing as well.
For my smaller size ultra fine ceramic stones in flat rectangular and triangle forms I'm using Lansky knife sharpening stones carefully pried off their plastic holders. For "surface plate" ultra fine ceramic polishing I've got a 2x10x1/2 stone I found at a wood working show many years ago.
For my India stone needs I've got an assortment of medium and fine India "files" that I've found here and there over the years. Lee Valley used to handle such things years ago but now they have other products that while suitable for wood working sharpening needs don't work so well for gunsmithing.
The lapping plates and diamond tools can work well too But for final polishing the ones I've seen so far can't hold a candle to a nice surface from a white ceramic stone.