You should always create different posts for different questions.
1) you can assign different FPM configurations to different step numbers. in the company code step, make all the sales fields read-only and vice versa.
2) the standard workflow will not make other steps obsolete. since you already built your own workflow you can achieve that by creating a 3-branch fork (which needs two branches to complete): one for executing the sales step, another for executing the company code step, and the third waiting for "rejection" event. once a processor (sales or company code) rejects, the fork terminates because a processing branch completed and the wait-for-event branch completed.