It depends on how much you really want to try to take on, I suppose. I'm not too familiar with knights on this server, but they do get access to a form of defensive discipline (kael gloves). Most of the time, where there's a will, there's a way, it might just be harder to use a knight as your main tank. For end game content though, I would probably veer toward warrior as a tank.
Bards are incredibly useful for increasing both caster and melee DPS as well as being able to pull.
Monks do good dps and get a clicky in tier 2 raid zones that allows them to pacify mobs for much easier single pulling.
Rogues and wizards are the DPS kings.
I wouldn't recommend just using a shaman bot, the bot will not have access to some of the nicer high end shaman abilities (E.g., panther). I also wouldn't worry too much about slow since there's like 3 weapons that proc slow I can think of off the top of my head, a slow clicky, and an aug that allows your weapon to proc slow.
Cleric is a necessity. Healer bots are questionable, but I think the logic is going to be worked on sometime or another.
I can't really speak to pet classes or zerkers so going to leave that alone.
At the end of the day, most people are generally helpful and friendly and, once you have a few toons to 70, if you decide you want to level up another one to help you progress more, it's pretty trivial to do. Feel it out, find a combination you think you would have fun with, and give it a whirl. There are some spots that are rough on the difficulty curve, so don't get too frustrated if you struggle (especially when you hit the level 55 zones and again when you hit kael).
You can basically solo to 70, so leveling shouldn't be a problem (At least, I solo'd my war to 70 with a cleric bot without much issue). It's the raid content and higher end content that really requires groups. Tiered zones are mostly instanced by guild tag (Ssra at tier 1 and pofire at tier 4 being the two exceptions), so when you decide you're ready to start trying out the raid content, you might want to join a guild or have one created for you and your wife.
Sorry, just sort of writing off the cuff. If I think of anything else I'll let you know.
And enjoy THF!

Cheers