Yes if you having that's great but alexa isn't show corrent traffic only count their plugin installed visitors only
Depends. 3000 is rank of some top page in a small country (non-english language). Anyway, this is not reliable enough to be so important. They are only tracking users of their toolbar.
My personal opinion... Any Alexa rank to make the top 100k is 'okay' and likely means the web site is starting to be developed and has some potential, or is already semi-established or could even be fully established in a very small niche. An Alexa rank under 10k would be great, and when investing in domains based on Alexa rank, I would hit for at least top 10k (if not top 5k) If you are on a higher budget, any Alexa rank in the top 3000 is awesome. You have to think of all the great established web sites out there. I am sure any of us can list 3000 of them, so for you to own or have the possibility to purchase one of those names is great. All the best, Jamie