it seems overwhelming, but it is easy really, just get a folder and put all of your documents in it with a few photocopies and go to immigration. It's actually very simple.
depends on your bank, in the case of Starling you get their rate on that day, its usually a fraction below the exchange rate (maybe 44.6 instead of 45 Baht, something like that). I would not use a bank card like Barclays or HSBC for this purpose or you would get a terrible exchange rate.
I don't think there are any pros to opening an account at this stage and you would pay annual fees.
Someone will correct me if there are some pros.
If you withdraw cash inside the bank with your bank card and passport you do not pay any ATM fees.
I would recommend getting another account/card in case you have any difficulties. Starling and Monza offer free overseas use. I use Starling and it's excellent.
this is the Wise app. It gives you the option to compare rates. It does not always show Wise as the best option. For example today it would be better for me to use Western Union to transfer British Pounds.