You shouldn't have problems, unless you are trying to bring a whole orchestra with you. Do expect to be asked about the kind of work you do if they do question you about it. Quite a few younger tourists bring musical instruments with them, guitars, and such. As long as they don't get the impression you'll be trying to make extra money on the side, you'll be fine.
In that time they could very easily raise the time of the banked money to six months, like in Hanoi. The time limits are changing monthly, and even weekly at some embassies, based on recent reports. They lots of times also want to see your most recent income tax filings.
the one very important detail you are missing, or simply forgetting, is that to apply for the type O based on retirement inside Thailand to get the initial 90 days, the bt800,000 must be in a Thai bank account in your name only. You can not use your foreign bank inside Thailand, and you can not get a Thai bank account on any tourist visa. You can use your foreign bank account balance if you apply outside of Thailand, like in Laos, Vietnam, Cambodia, Singapore, or Malaysia, but not inside Thailand. Lots go to Penang to apply.
The eye drops is the problem, as those are considered pharmaceutical products, and require an import license. You can not get the needed import license yourself, as you don't have a legal business. You need a Thai doctor to help you import them, if they are medically needed, and not available in Thailand. The UV sleeves you can buy in Thailand. Just refuse to accept the package from customs
Get separate type O 90 day visas based on retirement before you come to Thailand. This will give both of you the ability to easily get Thai bank accounts. First not all immigration offices accept joint accounts with the bt1.6million for your one year extensions the first year. Also, it is real convenient for you both to have a Thai bank account here, with most moving to scan to pay with a Thai bank account.
The BOI, board of investment, handles those visas, not the regular immigration offices, and they are very helpful, and easy to work with. You don't need an agent.
Any school, in order to qualify for the DTV, must be registered with the department of education. You might try the Wat Pho traditional massage school, or the Sunshine massage school, as both are registered with the department of education.
then get it. Just remember though, paying taxes in Thailand if you don't have to gives you no advantages in anything. Your home country, whether you like it, or not, I'm sure has tax rules that relate to what you are earning, no matter where you live in the world. Thailand simply wants you to be legal, to eliminate any money laundering thoughts.
that's actually too bad, because if you were American you would have the opportunity for a better business structure to set up under. How have you been getting paid, and where have you been living, while you've been working on the game? You will need to pay your taxes somewhere, and to do that in Thailand you will need a legal business, unless you are in fact working for some company not in Thailand/remote workers. At the very least you will have a tax liability in your passport country, not Thailand, unless you set up a legal business in Thailand. In your case to set up that business you will need at least bt2million in registered capital, and if you can't set up under the BOI, as a skilled worker, you will be required to hire, and pay, at least 4 Thai employees. These requirements are for your type B visa and work permit. At the very least, either way, you must have a licensed Thai accountant. There are no exceptions to this. You could get a DTV, Destination Thailand Visa, if the company you work for is legal, and will write you a letter stating you can work remotely, and most Thai embassies you apply at will want to see your last tax filing, plus bt500,000, or the equivalent, in a bank account in your name only. You can not do any of this as your wife's trailing spouse. There are ways you can do it, but it is not going to be free. It will cost you money.