What exactly are you claiming is getting more complicated?
Applying for a visa is easier than it's ever been. You used to have to mail your passport to the embassy. Now you just apply online in a few minutes and get your visa back in e-mail. That's incredibly simple.
Most immigration offices only need the TM30 to get the certificate of residency.
And you're not going to be applying for any further 90 day visa. You ALREADY HAVE the 90 day visa. The only option you have now is applying for the 1-year extension. Unless you're married to a Thai or have a half-thai Child, the 1-year extension is the only option for you.
You need to get a bank account opened and get the 800,000 baht transferred into the account in the next couple of weeks. If you're not able to do that, you won't have enough time to meet the seasoning requirement for the extension. The financial requirement for the 1-year extension is that the money must be in your account for 2 full months already at the time you apply for the extension.
If you're entering as a tourist, the rule is now and has been that you must be able to show you have at least 20,000 baht or equivalent in another major currency. It's incredibly rare to be asked, but if you are asked and cannot show it, you can be denied entry.
Look at the entry stamp in your passport. That's when you have to leave Thailand. Your permission to stay is in your passport and has nothing to do with your TDAC.
You don't need to actually go to the embassy. You won't even be allowed in. Everything is done online, and the visa will be a pdf that's sent to you by email
You choose the embassy based on where you are PHYSICALLY.
If you're in Laos, then you can use Vientiane if you're in the area that the Vientiane embassy covers, or you use Savannakhet if you're in the area that the consulate covers.
Same for Vietnam, when you're inside Vietnam you choose the embassy that covers where you are in Vietnam. They each cover different sections of the country, and it's best to keep to it because they can reject your application if your proof of location doesn't show that you're in the right location.
Also they can call you into the embassy for an interview so best to choose the one that's closest which should be the one covering where you are physically.
Something to keep in mind about Laos, the embassy and consulate there are the only ones that require you to go in person and pay after you submit your application online. That's not required in Vietnam or anywhere else except Myanmar.
As an example, here's the map of embassy and consulate coverage for the US.