You make $70 G at your regular job. I think that would be enough for you to buy a truck.
With three lawns I would not buy equipment but fix what you have including the trailer.
Being your are making $70 G a year you do not need to draw money out of your business. Just pay for gas and oil and small stuff as line for the trimmer. Then save the rest of the money to reinvest in the business. Including advertising.