@Peter ********
You have many things confused:
1.) You already have a Lao Visa Sticker, which was a Lao Visa on Arrival (Lao VoA) Sticker, that you had bought for USD $40 Dollars and the Lao Immigration Officer then ink stamped you in for 30 Days:
otherwise, there was no way for you to Make Entry into Laos with an Australia Passport without a Lao Visa Sticker in your passport beforehand;
2.) Apparently you have an UNUSED Non–O E–Visa that has not been activated yet which you have received from the Thai Consulate in Sydney
Now, all you have to do is show that PDF Print out (which you already did for the Thai Banks and Khon Kaen Immigration Office) to the Thai Immigration Officer on Arrival in Nong Khai
Then, check and verify that the Entry Stamp you receive from the Thai Immigration Officer on Arrival in Nong Khai gave you a Non–O Entry for 90 Days;
3.) You don't need any more visas from anywhere else and you don't need to stay in Laos for a few days and can just leave Laos now and Return Back and Make Entry into Thailand using that Non–O E–Visa issued by the Thai Consulate in Sydney;
4.) Once you have made Entry into Thailand and activated (used) your Non–O E–Visa, then you can go to a Thai Bank Now (there are some Thai Bank Branches open on Sundays) and open a Thai Bank Account;
5.) Don't bother going again to any local Thai Immigration Office (in your case, the Khon Kaen Immigration Office) without a Thai Bank Account already open and 800,000.- (800k) Thai Baht sitting in your Thai bank account for at least 2 months before going to any local Thai Immigration Office to apply for a Retirement Extension of Stay;
6.) Unfortunately, any and all Thai E–Visa's need to be applied for and processed:
a.) while you are physically NOT in Thailand, and
b.) while physically in the same jurisdiction (country) of whatever Thai Embassy/Thai Consulate you are trying to get a Thai E–Visa from
Unfortunately, that ship has already sailed now
It is up to the Thai Immigration Officer on Arrival at Nong Khai to make that determination about what to do or not do and at the full discretion of the Thai Immigration Officer (and, potentially, local Thai Immigration Office) about the specific circumstances of this Non–O Thai eVisa issued from the Thai Consulate in Sydney
(surprised the Khon Kaen Immigration Office didn't say more to you about your E–Visa from Sydney)
So, best of luck to you and unfortunately you have so many things confused, but apparently luck is definitely in your favor so far