I had one not long ago and I had booked a 90 day flight and the check in desk were perfectly aware that the visa could be extended by 30 days. I don't believe they will accept bus tickets but there are plenty of cheap flights in and out to adjacent Counties.
It happened to me earlier in January. If you look at your application on line it will tell you what is happening. On mine it said awaiting extra document, they had told what they wanted and I sent it less than 10 hrs later I had my visa.
Yes you can but you will probably have to leave and return to activate it. Flights in and out are dirt cheap plus you get a couple of days in another SE Asian Country.
You got a card to fill in, probably the sam cards that you used to get on flights. No landing cards so one has to register at immigration. That has been on the books for years but it seems most people just forgot about it?