having the nosewheel lower is not a good idea. What can happen is: As you pick up takeoff speed, you're sitting at a negative angle of attack, so the air is holding the plane down. If you don't apply up elevator soon enough, you can pick up enough speed that as soon as the plane rotates, it can leap into the air and stall.

It should sit level or very slightly nose-up

As far as how long they should be: Long enough for prop clearance, but not so long that they become "Spindley" or they will bend too easily