sixshot has made some excellent points.
Lots of questions for those of us who cast, & shoot a lot of handgun bullets.
I too wonder about the "8" barrel." Ruger made the .357 Maximum in 7-1/2" & 10". And T/C made them in 10" & 14". Not sure about the Dan Wesson barrel lengths, but it's possible they made the .357 Maximum in 8". That's IF I read your post & understood it to mean you have .357 Maxi guns in carbines, AND an 8" pistol.
And as noted by sixshot, using the Lyman/Keith bullet in most normal .357 Mag cylinders, it won't fit if loaded to the crimp ring. Some folks also will deep seat a bullet with the crimp over the driving band, and get good results. You could experiment with a dummy round to check lengths.
And powder coating, as also mentioned, I question the comment; "I know I will have to really clean the barrel with the powder coated bullets." Both sixshot,& myself as well as many others shoot a LOT of PCed bullets, & the cleaning is much easier & doesn't require the level of cleaning you seem to think.
And the use of the gas checks, (bullet cups) is dependent upon a few things. First off, the cast bullet will have it designed to where you can seat a GC or not. We call cast bullets by 3 basic types; Gas Check, Plain Base, or Tapered Base. In general, a GC design is often used in higher velocity bullets, cast a bit harder to prevent or reduce barrel leading.
Casting good pistol bullets can be both rewarding & frustrating until you figure out the alloy needed, for the velocity you desire & if the design requires a GC or not.
Slugging a barrel, checking chamber throats, matching the diameter of the bullet to the gun, and then shooting things to see what works best is a fun journey.
Again, as sixshot has mentioned, you should try to find a mentor to assist you in starting this if possible. It'll help the learning curve a lot by shortening it dramatically.