If you are designing an AC generator, you fist select a machine type, presumably a permanent synchronous generator in this case. Then you determine what you will drive it with. Perhaps you will crank it by hand. Then you estimate how much power you might be able to produce to turn the crank. That might be 100 watts. You need to estimate how fast you can turn the crank. That might be 120 RPM. Then you might want to look at some existing designs and determine how difficult it might be to design a generator that will produce 5 volts at 120 RPM. That might lead you to determine that you need to mechanically increase the cranking speed. There will be some power loss in the mechanical drive train, so you might have 90 watts mechanical input to the generator.
Then you design the generator. The generator will have losses that you should be able to estimate when doing the design. The rectifier will also have losses. I suspect that you would be doing quite well if your generator is 50% efficient. The rectifier will probably be 60% efficient. For 5 volts output after the forward voltage drop across the diodes, what does the input voltage need to be?
Two stages of of DC to DC step-up conversion will have a lot of lost power. If you are going to purchase those, see if you can get the efficiency from the seller.
