Please tell me if I am understanding this correctly.

Here is my situation: I am married to a Thai citizen. I am currently in the kingdom on a 30-entry stamp. I frequently have to leave the kingdom on relatively short notice (1-2 week notice).

I hope to apply for my Non-Imm "O" in Singapore later next month. I am taking my marriage certificate, House registration, Wife's Thai ID, and income statement, etc, etc...

I understand this visa is good for 90 days and then an extension must be requested for a 1 year "long stay" with 90-day reporting.

I know an "extension" visa can have a multiple re-entry for a small fee.

My question is:

Can my initial "O", NO extension, have a multiple re-entry?

My concern is that I pay "X" amount baht to fly to Singapore for my visa, and 1 week later have to depart for a short-notice job.

Thoughts and/or suggestions?

Yes. You can get a re-entry permit on any visa entry (not sure about visa exemption entries).

If you can swing a multi-entry non-o then you won't need a re-entry permit for 12 months

If you have 100,000 THB in the bank you better apply at Kuala Lumpur, they will issue a multiple non-O. As said, you won't need an extension of stay or a re-entry permit for 12 months.

Singapore will likely only issue a single entry, which you must extend at immigration and get a re-entry permit at the same time.

If you plan and qualify for one year extension of stay all you need is a single entry non immigrant O visa so one place is the same as another for that.

A multi entry non immigrant O visa from KL may be best as you plan frequent travel but will require proof of 100k in bank account.

If you need to travel before final approval of your one year extension of stay you should obtain single re-entry permits as they are only valid for the current permitted to stay time.

Silly question: Can the 100K be in my wife's bank? Or can it be in my US bank?

A US-bank should be fine.

Remember that if you want a 1 yaer extension of stay from immigration you will need to show 400,000 in a Thai bank account for at least 2 months in YOUR name only OR show that YOU have an income of 40,000 a month.

The wife's income or money in the bank is not considered.

Your U.S bank should be ok.

Great. Thanks to all.