[Olorin]

You don't even need to take NPCs for Quests. All of the big sidequests that involve NPCs (e.g. Nalia or Haer'Dalis) don't require you to have them in your party at any point. The smaller NPC quests that require them to be in your party can easily be skipped. Remember that when you are solo, exp gained is only divided by one person, so you will have plenty of experience even without doing every quest.

You could also consider a cleric/mage multi-class. They are a little weak at the start, but later on they get quite powerful--you can prep for melee by casting mage protections, then don your plate armor and still be able to use cleric spells in battle. Spell sequencers and contigencies can also be very interesting since you can put either cleric or mage spells in them (or combinations of the two--one small example would be link a doom and chromatic orb into a spell sequencer).