ACS with other metals

Yes - you can use other metals and materials with the Art Clay Silver products. The best material is Fine Silver [99.9% pure silver] this is because there are significantly fewer oxidation considerations when using it and firing the ACS. Sterling silver wire, sheet and findings will also work. I find I need to sand or abraid the surface abit to get a better joining. I usually use the Art Clay Silver 650 Overlay paste for my first layer. It seems to bond into the surfaces better. In the 2nd and further layers I use regular ACS650 paste. Sometimes I apply ACS and fire, apply more and fire again - this helps fill gaps and cracks which occur - usually driven by the 8 to 10% shrinkage that the ACS goes through. THis happens most noticably on the first firing. When I use Sterling, I usually try to cover the surface of the sterling completely - this seems to help avoid the firescale problems. Firescale is an oxide event that happens with the copper in the sterling alloy. Brass items can be fired in. I have done wire inclusions which worked great. I have not tried including a brass stampings or charms - this may require a test firing so you can check it out. I would be concerned about the oxidation of the brass as you fire.
With regard to using ring blanks as you suggest - this should work. I have not done this yet but I have Art Clay instructor friend who has, with good results. It may take multiple firings to get to your final finish. Firing multiple times does not seem to have any negative effects, I have done that alot. You may need to strategize your design so that you get some physical/mechanical connections between the Art Clay materials and your silver blank. Something like holes or wires or pegs which the ACS wraps around.
As a general rule I haven't found that ACS works well as an 'adhesive', it doesn't 'stick things together'. The ACS Oil Paste is better at joining in this manner but it fires at much hotter temperatures than ASC 650 products. [although it can be used to fire to used to join already fired 650 pieces together - they all have to be fired at the higher temps then]