You can increase just the nosewheel size if you want, however, the important thing is that the airplane sit close to level on it's wheels.

If the plane is strongly nose-up, it will be hard to land with out bouncing because the nosewheel will often touch down first, and it will have a tendancy to either take off before it should or "wheelbarrow" on takeoff. Wheelbarrowing is when the mains leave the ground, but the nosewheel is still in contact, often leading to a sudden sharp turn in an unpredictable direction.

If the plane is strongly nose-down, it will be easy to land, but hard to take off on a grass field. Nose down enough and the plane can accelerate to rather high speed with out lifting off until you touch the elevator, and the airplane suddenly leaps off the ground.

About the metal pushrod, you can do it, and many kits/arfs are designed that way, however it is possible to strip the gears of the rudder servo on a hard nose-first "arrival" (you know, not so much of a landing as a controlled crash into runway).
A metal gear servo will help with that, but then something else somewhere will break. However, if you work on landing smoothly, main wheels first, and work on keeping the nose "light" when taxiing and on takeoff, you won't have any issues. Basically, you want to hold up elevator when taxiing to take weight off the nosewheel. It also helps at the start of the take-off roll, but you have to get off the elevator before the plane jumps off the ground into a stall.