when I got a new account, I made a character of each class in nightfall and factions and did the first few quests (missions) with them just to unlock a few skills for the heroes you get in nightfall (so a warrior, monk, ranger and/or ele would be good) ...I did delete those toons since I made them just to unlock a few skills.... You dont have to keep your characters--so dont feel bad if you wish to delete a few of them (you get enough character spaces to make and try a few professions out).
what I would suggest is make a character in nightfall...and when you get to the secondary profession time---try all of the secondaries--talk to ALL of the other profession trainers (dont make a final decision on it!)...that way a few of each classes skills will get unlocked....and any skill that you have unlocked can be used by a hero with that class (primary or secondary).
and yeah, until you have unlocked some good skills heroes arent going to be very useful, the henchmen have full skills bars (well they have skills---)...so they will be better in the beginning.
where is the 'all you can eat' cookie bar?