The spell you start with (ember bolts I think it's called? The name escapes me) is actually pretty good; it has nice knockback to keep melee at bay and you end up throwing out up to 4 bolts at once you put more points into it. I'd say stick with that and pet skills until you can learn ember lance, which completely rips everything apart if you have the mana to support it.
I put most of my points into the arcane tree, with a bit of the battle tree for Ember shield and Ember Sentry, and my pet knows a 'summon skeleton' and a 'heal all spell'. I've found that my pet and her skeleton actually tank pretty decently (playing on Hard at the moment) - not incredible, but decent; considering what I've invested into it. This is with no points in pet mastery and no points in any summon skills for my character.
This makes me think that if you had Lore tree summons + Spell summons (skeletons) + pet mastery + gear that improves pet stats, you could build a pretty formidable army. I think once I retire this character, my next one is going to be more minion focused.
EDIT: That said, In the early levels of the game specifically, I really have no idea how well it would work. I didn't start using skeleton summons until after I had leveled up quite a bit.