Make sure you have the "3 proof ofs"...Proof of onward travel, Proof of accommodation and 20K Thai Baht or the same in foreign currency. You might not be asked to show this, BUT if an I/O asks for it and you cannot show proof, you can be denied entry into Thailand.
I would NEVER recommend overstaying a visa.....IF you happen to come across a police checkpoint and it is found you are on an overstay, you are in heaps of trouble....
There is no limit to the number of Tourist visas you can have, but you are advised to switch embassies frequently enough so as to prevent excessive "back-to-back" visas which might result in a dreaded "red stamp" which then bars you from using that embassy again.