@Mic***
I think he's right that if you push it over 6 months you will have issues. You would absolutely be able to do 60+30 and 2x ground border = 7 months the first time. It's when you fly back the next year to try that again, you could be questioned at the airport. Or if not the second year, the third or the fourth.
Or you may not, you may be fine. But it's a possibility. My feeling on it is under 6 months/year is the max that this will be reliable, if it's something you want to keep doing long term.
Definitely don't buy a condo if you have no long term visa, that makes little sense. With how cheap rents are, it makes little sense anyway, but makes even less sense if there's a *possibility* you'll be denied entry to the country, which there always is if you are spending a lot of time here on tourist visas.
I think if you keep it to 5 months a year, there is a very good chance you can do that indefinitely. Not 100% guaranteed, but as things are, good chance. Over 6 months, I'd suspect you will have a problem, at some stage.