Honestly unless you have access to what amounts to proper bodyshop-type spraying facilities this is going to be nigh-on impossible to repair yourself to any standard above "awful". There is extensive damage to the paintwork on the bumper, not to mention the full on crack shown in pic 3. You'd be much better off getting it done professionally or if funds are an issue (and you're willing to accept some drop in quality of the overall effect) then I'd try and track down a second hand bumper that's already painted in the right colour (ebay is a goldmine for that sort of thing)
1) As you can see from pics, there are white parts(I think thats the underlying plastic), non glossy black parts(I think thats the base coat of paint, is this correct?
Other way around - the "white" bits are where it is down to the primer. The dull black areas are the underlying plastic.
2) Im considering doing a quick job or doing it properly. Firstly if I just wanted a dead quick job, would I just go over it all with black paint( no need for primer or clear coat). Will it be ok to leave it like that if I'm happy returning to black is enough?
While a "quick job" will probably look better than the damage as-is I'm afraid to say that it will still look pretty awful. You won't get anywhere near a colour or "gloss" match and it will stick out like a sore thumb.
3) In pic 1, will a brush be sufficient for the line areas above wheel or do I need to cover above and below the lines with paper and then spray or brush those lines?
Hard to tell from just the photo but they don't look too deep, this is the one area where you may be able to achieve a decent result at home. A "touch up" repair kit may be sufficient - it will still be visible but will be greatly reduced. If you have the patience a decent wet sand and then polishing the life out of them with a mechanical polisher could produce quite good results.
4) Do the non glossy black parts, as in pic 2, only need a clear coat and wax over them? If not why since it seems the paint is intact except for the gloss?
No - see above. Those dull parts are actually the base plastic. There looks to be some areas where it's just the clear coat that's gone in pic 3 but it's hard to tell from pics.
5) For all white areas, I guess I just cover all good areas with some form of paper. Then any white areas need a primer, black coat, clear coat then wax layer and also smoothing out along the way. Is this correct?
They'll need a black coat + clear coat + smoothing + polishing + waxing. Even then they are probably still going to be visible, and you'll need a really clean and dust-free environment to do that in or you'll end up with clearcoat that looks like sand paper.