deploying in a month--is 6xx for me?

Drupal 6 is at Release Candidate stage, which means it is approaching release, but needs more testing. There are (as of a few moments ago) 10 critical bugs that need resolving.

If you'd like, you can help with bug testing through the Drupal 6 criticals issue queue.

There are a number of changes between 5 and 6, so modules will need to be updated. It depends on the complexity of the module as to how complex that upgrade may be. Updating your modules and updating your themes information is available. This page has an update of the D6 status of many modules.

Take into consideration that it still is an RC, and that there is no guarantee whatsoever that you will have a release of 6.0 in under a month. And even if the final for 6.0 is delivered within a month, it could still be that certain modules that are not part of the core are not yet ported, or not ready for deployment on production sites....

If the site your deploying in a month is a site for a client, than personally I would not go for 6, but try to set the site up as dual-version as possible.
All configuration done to 5.5 can be documented, and replicated to a wide extent in 6.0, but if you're gonna do custom work in 5.5 (eg. write your own specific modules) that you have to keep in mind that there can be stuff that needs to be ported to fit the changes that are in 6.0.

A very good place to start would be the handbook for both versions, as they almost certainly contain a list of changes to make to your custom work in order to make them work under Drupal 6.

So my advice in this would be, think very hard about whether or not you NEED the functionality that is in 6.0...
Sure, it's all very sweet and tempting, but would you sell something to a client that you have not even tasted for yourself? ;)