Legally, any property owner in Thailand is required to report the arrival of a foreigner within 24 hours. This is doing through the online TM30 system or in person at the local immigration office.
Realistically, if you don't plan on going to immigration at all during your entire stay in Thailand, then you won't need a TM30. The TM30 is only needed when getting some type of service from the immigration office.
The requirements of your extension were as follows:
1) Must keep your account at 800,000 baht for 3 months after you received your extension
2) Your account must never drop below 400,000 baht at any time
For your next extension you must have your account back at 800,000 baht for 2 full months before you apply for your extension.
Part of your application for your next extension will be a 12 month bank statement, and the immigration officer will check your bank statement to see that you maintained the requirements from last year's extension. If you did not, they will deny you applying for a new extension and you will have to leave Thailand and start over with a new non-O visa and extension.
Alternately if you don't want to start over, you'll need to use the services of an agent to bypass the financial requirements.
It will likely still be an immigration officer that is making the decision on the ETA. So you'll know if you are allowed to enter before you travel to Thailand yes, but you'll still be at the mercy of an immigration officer same as now.