1 StP will be capped at second level spells for this, lacking the fourth level powers known. The same goes for extra slot, extra spell, and expanded knowledge. Forgot to consult the handy E6 stuff, which appears to overwrite the feats I was basing my thoughts on, carry on.
2 Hmm...to account for zero levels spells it shall be reworded as...'per minimum erudite level to learn each power'. First level powers and zero level spells are 20, second level powers and first level spells are 60, and third level powers and second level spells are 100.
3 Nope, the erudite is limited by unique manifesting, which you are still doing with the second power from linked power.
4 Yup