I use Z for plurals exclusively; that's one common system. You might be interested in my post: https://blog.waleedkhan.name/my-steno-system/#orthography

For homophones, I use a different vowel (OEU = oi, the least used vowel sound; AE is an extra vowel sound not representing anything). For proper vs common names, i often duplicate the stroke (e.g. MAT = "mat", MAT/MAT = "Matt").