No probs, I have had less than, 30 days and more than. But it is usually 30 days. That is the norm. :) They are a law unto themselves....555. I did the same as you; got a Single re-entry, returned before the consideration date and used it. Got the rest of the time stamped in, and got a multi re-entry.
That's seems exactly what you asked. As Graham said. 1000 baht. Re-entry. Get extension. Another re-entry. Immigration can put whatever date they like for the under consideration period. Sometimes less then 30, sometimes more.
I would recommend to you, in future, that whenever you get an extension of stay, get a multi-re-entry on that same day. This is what I do, so I never forget.
No limit, but someone having a bad day will apply one. Avoid female Immigration Officers. In my experience, they are most likely to give you problems. Not being sexist, just factual, and based on experience. If you plan to stay longer term, with more visits, get a DTV or similar.
Ah right. Under considerstion for extensions are definitely fine to leave on and return. I did this last month, with a re-entry, with no issues. In Pattaya, a home visit is required. Not sure on other offices.