You can boost the LED light with a fresnel lens to some extend. its a tiny version of the kind of lenses they have in light houses.
LED brightness, they are brighter if you run more current through them but you quickly reach a point when they burn out, better stick to the maximum current on the spec sheet for your particular LED.
Battery consumption, for a given brigthness you pass a given current through the LED. 10 LED's consume 10 times the current, there's no magic unless you start pulsing the LED's rapidly. That way you deceive the eye to think they are on all the time. You need to pulse around 50 Hz or faster or you will see flickering. You could reduce power consumption by half with that, at the expense of more complexity.
Have fun,
Klaus