Help Me Build The Perfect Mountain Bike

I'm in the market for a bicycle. Not to replace any of my motorized vehicles, don't worry, purely as a supplement. I'm looking for a fully rigid mountain bike that's on the small side, with not very many gears and some style. Peddlers of Oppo, help me out here.

My specs; I'm 6' and about 165 pounds.

I'm looking for a bike that's tough enough to do pretty rough trail riding in, but it doesn't have to do it fast (tried downhill, too scary). I want to go full rigid because I don't want the weight of a shock which will be largely unnecessary for the majority of the riding I'm going to end up doing in real life (rail trails with an ice coffee in one hand).

I want a frame that's small because I'm never going to ride long distance or competitively but I like to be able to throw the thing around when I do hit the dirt. Was also thinking single speed crankset and nine-speed cassette for one less set of wires (can bikes even be set up that way?)

FWIW, I did mountain bike quite a bit as a youngster and did race, so I know what terrain feels like. And I am mechanically inclined enough to put a bike together, the question is whether I'm motivated enough to order parts separately.

I'm not brand loyal but it does matter to me that it looks cool, so I'm looking for suggestions and answers to these questions:

  • Brands I should avoid?
  • Components I should splurge on?
  • What kind of money buys what quality?
  • ...Anything I might be forgetting?