Will I face issues with Thailand immigration without a return ticket and while applying for a marriage visa?

They will ask if you have had a extention before.

The airline will likely ask to see onward travel, you can always book a cheap flight, you can usually find ones to KL for quite affordable prices. Then again, they might not ask you. If they do ask and you don’t have it you could be denied boarding

You USA marriage doc is about as good as a ashtray on a motorcycle. If you are hoping to apply for a visa though marriage do it in your home country. There are a lot of items you need to get sorted while in Thailand if looking for extension on the Non O though marriage. It takes time and a bit of work, I would speak to immigration once you arrive and with wife.

Asking your Thai wife to look into this should be easy for her

TDAC means you are coming. Has nothing to do with imagration. Your airline is the one that you should worry about. They might not let you on the plane

Hopefully, I can save you some time the US Embassy has form online to create an affidavit. Create the affidavit, including all of the pertinent information about your marriage time place date preacher’s name how you met and when you got married anything that would be pertinent. Take that affidavit to the US Embassy and get it notarized then go the district office where your home is located with a translated copy of your marriage certificate from the United States and your affidavit and then they will fill out the proper paperwork for you  to register your marriage . I know this doesn’t answer your question directly, but it it will help you to register your marriage which you will have to do before you go to Immigration.

Your TDAC is an electronic arrival card it has nothing to do either with any visa or length of stay

If you appear to be a good citizen they dont ask for return ticket or how much money you have. The money shouldnt be a problem anyway, since its only 20,000 Baht($600) The problem now is tourists that overstayed. They are tired of people playing games with their immigration laws. People that overstayed or have done alot of Visa runs are now being denied entry. If youre coming in on the 30 day Tourist stamp, leave it at that. Dont tell them your life story or about getting any more Visas to stay longer. It will only complicate the situation. Its easy now, just the TDAC form, passport, and youre in. Dont talk too much.

There will be a full body cavity search upon arrival..

$ 100 one way ticket to Ho Chi Mi City

You never know! Chances are they won’t even check it but the airline is far more likely to.

As you are looking at a marriage visa, why not apply for the non O visa from the Thai embassy in the USA? Then you have no issues as an onward ticket isn’t needed.

No

I’ve been to bangkok last year and I have 60days stamp, under visa exception.

But i still have the same question, is it okay if we book our onward ticket later while in Thailand?

Just go online and book the cheapest bus ticket to Laos or a cheap flight to Vietnam or another Asian country

I've answered the ticket issue in your other post. The marriage visa is a 90 day Non-O visa and in order to apply for it you must have 400k baht in a Thai bank account in your name. If you don't already have a Thai bank account apply for the 90 day Non-O visa before you travel to Thailand. Once here open a bank account and deposit 400k baht which must be in the account for 2 months before you can apply for a 12 month extension of stay.

It also appears that you got married in the US and not Thailand so there are some additional hoops you need to jump through to obtain a kor ror 22 certificate which you need for the extension of stay (or the Non-O if you already have a Thai bank account)

To obtain a Kor Ror 22 (Registration of Family Status) in Thailand, which records a foreign marriage, you must legalize your foreign marriage certificate in your home country, translate it into Thai, have it verified by the Thai Ministry of Foreign Affairs (MFA), and finally register it at a local district office (Amphur).

I doubt the thai authorities will ask you for your flight out but your airline might especially since you dont have a visa, more often than not its the airline that checks since they are accountable for your return if you fail entry. You dont need to fill in the departure date or flight in your tdac it is not a mandate field marked with * asterisk. I assume you must be flying very soon?! Have you entered thailand many time previously on visa exempt?

Maybe you could get the non O before travelling. It's the airline might ask for proof of leaving if you intent to go with no visa.