I just installed SPlat as an intermediate step in my move to CbB. However, in trying out SPlat, I am having issues - I can run old projects, but if I save and try to run again I get a fatal error. Should I just ignore this and move right on to the CbB install and forget about SPlat, or should I fix/reinstall SPlat first?

Since both can be installed side by side, maybe install CbB and see if it runs smoother. It will run the old projects and import your plugins from SPlat.