The UK microlight licence is the NPPL(M); in theory you can upgrade to an NPPL(SSEA) - "Simple Single Engined Aeroplanes" in about 3 hours, in practice you're likely to need 8-12. Probably a bit more if coming off flexwings.
"Fixed Wing" is a common euphemism for 3-axis microlights, "flexwing" is the common term for weightshift controlled microlights.
The NPPL(SSEA) will limit you to day-visual conditions, if you want to fly night, or on instruments, or with more than 3 passengers, then you need to upgrade further to the "JAR" licence which will be a lot more exams and a longer flying course.
You can earn your living in microlighting, usually from a combination of teaching, hangerage and maintenance support. The income is not fantastic, but generally better than teaching on light aeroplanes.
Much of this terminology is likely to change in the next year or so, but the basic facts won't.
G