You'll get a lot of negativity on here mate, but please be careful. It could go well for you but if she isn't the right person, it will possibly end in disaster. But I wish you well.
I've carried out maintenance on my property, cut grass, tended my goats in the fields, plus cared for other personal livestock, duck, fish and chicken I've even ploughed fields both on my property and my mates property. Never had a problem. This is over a period of over 12 years. As long as it's your own stuff it seems to be ok, and nobody appears to be bothered. Even if I possessed a work permit (which I don't) I can still only professionally do work that a Thai cannot do. That's the law. But Thailand is Thailand.