How far?

The range limit of a Microlight depends on it's fuel capacity and consumption, coupled with the strength and direction of the wind, and the capacity of the pilot's bladder! e.g. my Kiss 400 has a 60 litre fuel tank, and consumes about 13 litres per hour to cruise at about 57 miles per hour. So assuming I want to land with a reserve of 5 litres (of which, in my tank, the last 2 litres are unusable anyway), I can cruise for 60 - 5 = 55 / 13 = 4.23 hours At 57 mph that allows me to cover just over 240 miles in still air. Now if I have a 20 mph tail wind, my speed over the ground increases to 77 mph, allowing me to cover 325 miles. The longest I have ever spent airborne in one period is 4 hours, and I was damned glad to get out of the plane at the end of it!

How high?

In the UK, in unrestricted airspace, the maximum height you are allowed to fly without filing a flight plan is 10,000 feet. This is plenty high enough for most people. My personal 'best' is just over 14000 feet. Note that when I did this, I was in constant radio contact with friends flying far lower, and they kept getting me to do sums, so we could spot any onset of hypoxia (discussed in detail later in this thread). Fortunately for me, there was apparently none.