rehashed

I am in the final throws of launching my startup. A name has been chosen (which I have grown quite attached to), and now its time to address trademarking. Its a bootstrapped startup, using what time and money I can save from my day job, and $18k+ with single-class global registration is so far out of my league I was wondering:

1) Is a trademark important in this day and age? I already hold the domain - isn't that enough?

2) If i DONT have the trademark, could someone else register it and stop me trading under that name?

3) As a generic web application, what classes and communities should I be targeting to get good coverage for the least expense?

4) What sort of protection do other HN startups tend to go for when launching their products?

I am selling a few domains that I havent gotten around to using in at least a year in order to help bootstrap my startup.

If theres anything you are interested in please feel free to make an offer! Your interest would be greatly appreciated and will help me fund my venture!

Kind Regards,

Matt

  *GTLD:*
  - appscale.net (idea: web services for apps)
  - appscale.org
  - energymind.com (my old consultancy)
  - godspire.com (idea: javascript MMO i never got around to starting)
  - heyreddit.com (was a popular chatroulette thing for reddit)
  - mediaparty.com (idea: deviant art for all media)
  - wordflows.com (idea: CMS platform)
  - wordflows.net
  - wordflows.org

  *UK:*
  - brokersmart.co.uk (idea: CRM for brokers)
  - cardiffmedia.co.uk (idea: Local consultancy)
  - cashhappy.co.uk (idea: finance comparison)
  - deyon.co.uk
  - digimall.co.uk (idea: multi-store marketplace)
  - energymind.co.uk
  - smartbroker.co.uk
  - wordflows.co.uk

  *MISC:*
  - dart.ws (idea: forum for dartlang)
  - snapshot.ws (idea: webpage screen shot service)