Welcome.
As for Class selection, the biggest thing that most will tell you is to pick a class you love playing. That will make the level grind easier to swallow.
Bards are a great class to play. They are arguably the most difficult class to play very well. Because of this they are a little rare and at high levels that may make it easier to get in to a full guild because they may not have a lot of bards.
Clerics are always welcome in groups and you can't ever really have to many
[You must be logged in to view images. Log in or Register.]. It may be hard to get in to a hardcore raiding guild because they usually already have their top clerics in place and the class full. That doesn't mean you won't find a guild that you will have fun in. Clerics can get a little boring to play at higher levels especially in classic because you just sit/stand/complete heal/sit rinse and repeat but it does get more exciting after Kunark release.
Warriors...well you know the drill here smashy smashy but in classic they could not keep agro very well so you may not be the most desirable tank. There does seem to be a lack of tanks on the server though so you shouldn't have too much trouble finding a group.
There are also the XP penalties to consider. there is a race and class XP penalty/bonus system in classic. EX: As a warrior you have bonus XP but most of the classes that can be warrior have a penalty. See below:
By Race:
Troll -20%
Iksar -20%
Ogre -15%
Barbarian -5%
Halfling +5%
By Class:
Paladin / Shadowknight / Ranger / Bard -40%
Monk -20%
Wizard / Magician / Enchanter / Necromancer -10%
Rogue +9%
Warrior +10%
But seriously just play something yo9u like to play XP penalty or not. It will make things a lot more fun.