welcome to the board Barry,
Don't worry about going over on amps. Your motor will only pull as many amps as it needs, no more (you can usually feed it more volts than it says too). What you'll need to watch out for is the rated voltage of the controller. That is the major sticking point for most EV setups, the controller. If you need a bigger/better one for what you're doing you can always find one
online. 100 watts isn't too much in terms of power for electric bikes, but you could easily up that by using a 36v controller and running your motor at 36 volts.
Anyway, keep looking around at parts, and reading about electric conversions and you'll be in great shape.