I assume you want to be able to purchase new equipment for cash over the years and you're asking about a savings fund for that?
You're a solo guy...if your route is tight I'd say your break down should be...
50% your pay
25% expenses (gas, ins., trimmer line, oil, etc, advert,break downs)
So, lets say you bill 5k/mth
Your pay is 2500
That savings may be a bit high as you wont need new stuff every dang year...so you can tweak that
14' landscape trailer
60'' Exmark TT
21'' Personal Pace