Short games / solo?

Hi,

I haven't played wow before but did spend a couple years playing everquest in the pre-wow days. Since then I haven't touched mmorpg.

I would like to play but my uninterrupted play time is generally under an hour.

I started the free trial as a holy priest and managed to get it to level 17 by doing the short quests and messing around in the zone where quest was.

Is it worthwhile to play solo given my time constraint? That is will I only be able to see a fraction 10%, 20% etc of content? I may have not chosen the best solo class but I'm just exploring the classes.

I haven't tried a dungeon yet but do I need to buy the latest expansion for solo dungeon?

What do I need to buy? The subscription + latest expansion? Or just subscription?

Thanks