You realize a fairly athletic youthful human is good for maybe 200-250 watts to the pedals for maybe an hour or two?
Pro level outputs are on the order of 400+ watts for 30-60 minutes at the top end, ie best 10% of the peloton.
As to the generator you might want to burrow into the characteristics of small wind power generators, ie what makes
them work at sub 100 Rpm ratings. They seem to be similar to car alternators, ie 3phase low voltage output but at much
lower rpm.
250 to 500 watt-hours will fully charge a good-sized battery. This is plenty to run a small computer (e.g. Raspberry Pi or One Laptop per Child) for a full work day or light a small house all evening with LEDs. A 500 watt-hour battery runs my small ham radio station for in excess of a day.