Taxes roughly 20% of gross
Put replacing all your equipment (or upgrading) in your prices per hour
charge a per hour rate for all your services, make sure this rate covers everything from labor to equipment, taxes, licenesing, fuel, insurance etc.
Pay yourself LAST & invest in yourself and in your business. Dont take jobs if your making less than 15% profit. do the math on your profit margin and try your best to keep it at 20% consistently. Sometimes higher, sometimes lower depending on the market and customers needs. Thats where your discretion plays a part in your business and you can decide what you need to charge
Everything you buy for your business needs to come out of someone elses pocket essentially. You shouldnt be buying anything thats not an asset to your company and charge for everything down to your trimmer line. Get every breakdown in expenses on paper, so you know BEFORE you get in over your head.