I found a pretty good elven shield that I carry around but I mostly keep one hand free for constant magic attacks. I love conjuring an atronach, casting sanguine rose for a random dremora and then relying on my power and Lydia's backup to ruin the field of battle.
I am thinking of getting a new companion because I have accumulated like 5 or 6 now to choose from. My concern is the potential loss of carrying power as Lydia is a mule (she can carry over 220 for me while wearing full dwarven armour). I do also exploit her character a touch by not giving her a shield as she carries one by default.
So far, my best record was having 2 conjurations and 2 npc's fighting on my behalf in some dungeon near markarth but I could have had more except for the fact that too many NPC's clutter the lines of fire and they can get glitched in dumb places.
My number one tip is to improve your merchant skills with all the potions, altars, enchantments and perks. Money is far rarer in Skyrim than it was in Oblivion and it really changes the game on you, the best stuff comes in treasure boxes (u need the map first) but you can always buy what you want, when you want it.