I just went through getting a marriage visa through the online portal. I have a state pension from Oregon. All I had to do was go to my portal on the state pension website and they had a statement much like my bank statement indicating what payments they have made and when. It was available for download as a pdf. So you might check to see if your state pension office has such a portal.
Change $100 at a money exchange. The Super Rich money exchange usually has better exchange rates. You can find out the nearest location on Google when you get there. Just use Google translate which is in Chrome, to change the page to English. Make sure you take only new $100 bills, the kind with the ID strip and hologram. Keep them new and flat (they love no creases, bent corners or small tears) for the best exchange rate. Second best, but with some fees attached, is to use an ATM at a bank in one of the zillions of malls or Tesla Lotus market places.