I would put most of your effort into Marketing but capitalize on the word of mouth and reviews and adding to your Google profile at least once a week. Nothing fancy - a picture of a mower with a little caption, a picture or video of a completed job - things like that. These aren't high-cost items - all of this is free. I'd also work on getting into the facebook groups in your area and self-promote - not like crazy but when people are saying it - link them to your Google Profile or your website (if you have one). If it were me doing it, I'd use Jobber's marketing suite they have great templates for a super simple website and requests for quotes are all captured right there and it integrates really nicely. What's good about that is that it really helps you compete with the larger companies and helps to present a more professional image. That would be where i spend my "marketing" budget - but you'll be doing that in your off time or perhaps a close friend or family member can be the one out there on FB recommending you in those groups, etc.
I wouldn't recommend getting the LLC off the rip but I'm not a lawyer so this isn't legal advice. You can usually register a ficticious name for around $50 or so and then it's free to get an EIN. I'd just set yourself as a sole proprietor but open that business account so that you can accept credit cards and it's CLEAN.
To me, the most important thing to invest in is your data and your brand. You can always get new equipment down the road, expand marketing efforts, hire more people, transfer your Sole Proprietorship into an LLC, but you need to be collecting information from the people you're working with now and even the people you're quoting but not winning the job. WHY? Because that becomes invaluable as a warm market to promote products/services/specials to. I'd spend MONEY on my systems. Jobber's not paying me to say this (Hi, Jobber lol) but getting your Jobber subscription running and adding on some of the things you don't think you need but they set you up for success - like the Marketing add-on. Get your bookkeeping in order (Jobber syncs seamlessly into QB and I can help get that all set up if you need). Promote promote promote your business on Google and Social platforms. Social platforms for your 'warm market' - people who already know and like you and will recommend you; and Google My Business for those who aren't direct referrals but heard from a friend of a friend. I truly hope this helps and if you'd like, feel free to check out my coaching services at http://www.homeprocoaching.com