tm30 is what you get from whoever that you rent from once in Thailand and they file that with the government for you at least my agent filed it for me. I came with the intention of staying long term but after all the run around I received for a visa I have decided its not worth it to me and im pressuring a country that better suits me.
Once you reach around about 6 months in one year you're definitely at risk..I personally wouldn't do it. Apply for the tourist visa online and see if you get approved before wasting big time and money. Then you can know for sure before you just show up.