You can enter as many times as you want for a holiday. 4 times a year for 2 weeks for example will be fine. TAT want you to come ans spend your money here, and then go home and save up again!
The updates are for extensions and border runs to prevent long term abuse thats all
Overstay starts the day after your visa/exemption expires. 500 baht a day up to 20,000 baht. No affect if less than 90 days. However, if you wish to get a DTV or similar in the future the application asks if you have ever overstayed. This may result in a DTV rejection so try avoid overstaying if possible.