no one can answer this for you - it depends on the source of the money, whether you have already paid tax on it (or earned it in a year you were not tax resident if you are a new tax resident), whether your home country has a DTA, what exemptions you can claim. It is complex but there is enough content around (including youtube) that will help you get a feel/estimate.
A bank certificate is an official document the bank can provide to verify the amount of money you have - essentially the same as a statement but they produce it. I just gave a bank statement and it was fine.
I applied in London - didn’t have to be there - just in UK. I think you will struggle with the entry stamp point - you need a utility bill, or bank statement with your name and address. Not sure about the poker point - I would submit contract etc and see if they ask.
ah ok - fair enough - you meant to jeopardise your ability to explain the process to people when you have done it yourself. The original post read a little differently (just some friendly feedback!). Good luck - I have a completely lazy mindset about these things and agents than you clearly! Cheers
Genuine question - why would using an agent jeopardise your position? I spent my entire career in Finance but use an agent which is perfectly legal and proper.