Basicly Cooledit Pro contains all the tools you need for mastering.
In other words you can master yourselve.
BUT....
CoolEdit does not provide THE EARS and Experience of a professional.
Which can be a good reason to go to a studio.
An experienced professional will master in a way that the production will sound decent on any device (transistor radio to 100.000,-- equipment)

Thing's you don't do and thing's you will have to avoid before mastering!;

1. Do not normalise!
2. Do not use the limiter
3. Avoid clipping/pops (watch the record level!)
4. Try to record as clean as possible
(start at -15 db if you have 3 or more tracks)
Too loud recorded is not really reversable and will destroy all dynamics and headroom
the studio needs to master well.
5. No equalising.
If a track needs equalising it means the
record settings were wrong.
6. If the professional studio has Cooledit software, do not mix down and leave all tracks in tact.

Ofcourse I would recommand to experiment with the mix down untill you are satisfied with it, but make sure you save the original tracks each time!
Then when you are satisfied take the mixdown and the separated tracks to the studio.

Fred