So long as those coins are stamped 999.99 silver it would be fine.
Using run of the mill silver coins is a very bad idea as they are an alloy of silver, not pure silver.
You have to use pure silver to make CS.
Iv'e been making CS since about 2000. Everyone has their desired method. This is what I do:
I use any old DC transformer and have made it successfully (some 500 gallons and counting), using voltages that range from 9 volts up to 27 volts.
I use an old pickle jar that I fill almost to the top with distilled water.
I suspend the silver ingots using 4 chop sticks that I have bound on each end using rubber bands so the ingots are wedged between the chop sticks and won't slip.
It takes longer to make your first batch, so use a red laser to check your progress. When I see a nice thick beam of laser light, I call it done.
Save some of this batch to seed your next batch, which will make the process go much faster.
To make the golden colored CS (which I believe to be superior to normal CS, I unplug the transformer (so no electricity is flowing through the ingots), and I leave the bars suspended in the CS for several hours.
The water takes on a golden tinge (sort of like urine), but for reasons beyond my ken, it is much more effective than the "normal" CS.
HTH.
I found this out by accident. One day I was in a rush, and unplugged the transformer. When I returned, the batch had that yellow tinge to it. At first, I thought I ruined the batch, but as it turned out, I ended up making the same stuff that people go to a lot of trouble, using microwave ovens, etc.
I was as shocked as the next guy. But it works.
Use a red laser. Green lasers are too strong, and you will see the beam in the water, even if there is nothing to see, if you know what I mean.
You can't see the red laser in the water unless there are silver ions present.