Thanks. My work HR has advised just getting all our extensions to 27 Oct instead of 30 Nov. Makes sense, and at least it's only a month less. My fault for not noticing his passport expiry date!
There's no limit, but letting you in is at the discretion of the IO. If he/she suspects you're 'living' in Thailand you can be denied entry and told to get an appropriate visa. Chances are, you won't have a problem next time. If you're concerned you can get a Tourist visa.