Welcome to Orchid! I’m sure you’ll enjoy it.
You didn’t say what you wanted to do with your tumbler; polish
(burnish, really) or use it to cut down rough edges etc. The media
used will vary depending on the job.
I’ve found the vibratory tumbler is the quickest & most economical
for most jobs. For burnishing, assorted shapes of stainless steel shot
work the best. They get in all but the tiniest of spaces. Both carbon
& stainless steel shot is available. The stainless costs a little more
to start with, but it won’t rust & maintenance is lots easier. It’ll
last a lifetime. Carbon steel shot, about 1/2 as costly as stainless,
but it rusts & may have to be replaced if it gets pitted.
For cutting rough edges, ceramic media will probably be your best
bet. It kind of depends on the roughness, material & degree of cutting
Vibratory tumblers come in many sizes starting with about a 10"
diameter bowl going up to about 24" diameter bowls.