Grab the Gold Box edition quick if you can find it. Platinum addition (including Foundations, TOA and New Frontiers) is due out the end of June so I doubt they'll be issuing many more copies of the Gold Edition.
The problem with DAOC at the moment is that many servers are underpopulated. With the population split between 3 realms, you can end up feeling rather alone, especially during the lower levels.
The best place to start experimenting with classes is on Gaheris. That is the cooperative server. You can make up to 24 characters on Gaheris (8 in each realm) and travel between realms, so with someone's help, you can transfer things you accumulate between characters to give yourself a head start with a new character. People tend to be friendlier on Gaheris - the broadcast channel is used more freely - so you can also garner more tips about playing certain classes.
The problem with Gaheris is that there is no RvR, which is the keystone of DAOC in later levels, so if you like the idea of battling players from other realms, you'll need to join a regular server. No, you can't transfer characters from server to server, so you'll have to start fresh. Playing on Gaheris, you'll be able to determine what realm's classes you enjoy most and make a smoother transition to a regular server.
Things you want to look for on a regular server is a balanced population between realms (camelotherald.com and hit the realm wars tab). Most servers seem to be relatively balanced these days, so that shouldn't be a problem. The reason you want a balanced population is so, hopefully, RvR will be fun rather than one realm dominating it.
Join a guild as soon as you can. Doing a /who in the newbie zone during the times you expect to play most should give you an idea of which guilds have a presence during your play times as well as those guilds which have players around your level. Joining a guild has many interpersonal benefits. Experienced players can give advice and help you out with low level items. You gain an instant "social circle" and always have folks to talk to.
As far as newbies go, most older games suffer from a lack of newbies after a couple years. The new trend seems to be to release a combination pack of all previous expansions. That may begin to alleviate this problem because a new player will only have to buy one box instead of many in order to be up to date.