I'm not a CPA, which is who you would seek for this advice, but as far as charging for the service of mowing, there are no taxes to collect, so taxes you will pay are income taxes (self employment taxes), if you are selling goods though, you will have to collect sales taxes. I have an LLC so I also pay a fee for the LLC every year. You may have to pay local taxes as well, where I am we do not ever go over the minimum which is $50. As far as "write-offs" you can write off pretty much any expense you have with the business. Just keep really good records and let an accountant do your taxes. Not sure if we can suggest services on this site, but I use www.waveapps.com
for my accounting software because it is free and has an iphone app to take photo's of receipts to keep up with them. Hope that helps.