With silver thyings are different. I just recently tried to do some sterling silver and nickel silver mokume and had mixed results. Doing a straight laminate is easy and everything will start fuse at around 1432 °F which is the eutectic temperature.
Above that temp the sterling is semi-solid or "solidus" which makes twisting a real pain in the butt. Trust me I have ruined about $200 worth of sterling trying to twist a billet too hot and getting delamination. It just doesn't work well. I think the only way to work it would be at a dull red heat around 1200 °F, but then it is more difficult to twist in larger billet sizes.
But there are differences between fine silver (pure), sterling silver (7.5% copper) and nickel silver (copper, nickel, and tin). Silver/copper eutectoid temp is 1432 °F, so if you use fine silver with another alloy that does not contain copper, you can work at higher temps. Even with fine silver next to a copper bearing alloy will creat the eutectic alloy and start to get mushy at 1432 °F.
Most of my experience has been with copper and nickel silver. They fuse at about 1880 °F (according to my pyro) which is a pretty high temp allowing to to be able forge and twist after the initial diffusion bond as long as you keep the temp below the fusion temperature. I have never had much problem with twisting or forging Cu/NS mokume. Just watch out or the edges cracking when you twist.
I have just recently started trying new alloys like sterling silver with NS and making titanium mokume. Unfortunately all that is pretty expensive just for raw materials and they all have the eutectoid thing going on which makes forging and twisting a PITA.
As far as the jelly roll pattern, you will just need to keep pressure on all sides of the roll to get good fusion to make it work. Since the bond works from clean surfaces, under pressure, at high heat, without oxygen, you can't just heat it up and smack it with a hammer like we do when making damscus steel. Everything needs to be set inplace and ready once you put it into the forge to fuse.
I would highly suggest the Steve Midgett book if you don't have it already. You can get it from his website
www.mokume.com He discusses all firing techniques and has an alloy compatability chart which is pretty useful.
Other than that get your metals clean and don't over heat and all should be good.