It's likely the instructions from the embassy say to print the visa and hand it over with your passport. For Thailand, you always want everything printed. You probably could get in without it printed, but you would need to make sure the passport control officers understands you have it because there's a risk of you being stamped in incorrectly without it. You'll still need it printed later anyways for your extension and possibly for your bank.
Generally Kasikorn or SCB due to the increased transfer limits from Wise to those banks. Bangkok Bank also has an increased transfer limit but that bank is best to be avoided for now.
In the end though, it's whatever bank will actually let you open an account that is the best one.
you can't show because it doesn't exist. There is no such rule. It's a BANK policy made by the banks. Not a rule they have to follow. It's their decision
The visa itself is valid for 90 days. That means you must enter Thailand within 90 days before the visa expires.
Once you enter Thailand, the visa then determines how many days permission to stay in Thailand you will receive. A Non-O visa grants 90 days permission to stay, so you will receive a 90 day entry stamp. Even if you enter Thailand on the last day your visa is valid, you will receive a 90 day entry stamp.