a reentry permit only keeps your 90 day visa active to the expiration date. You will have to return before that date or you will have to start over again.
unfortunately we cannot make assumptions in Thailand because every government agency has their own interpretation of the law. Good luck and I hope you get your visa.
If you are staying with your son have him do a TM 30 showing that you live with him. Having a Non O visa already should make it easier to get a bank account. Just make sure you get a Certificate of Residency from Immigration when the TM 30 is approved.
Everyone just needs to read the Double Tax Agreement between your own country and Thailand. For US Citizens I know for sure Social Security and any other Federal Pensions are not, I repeat not taxable in Thailand.