I think your idea is good, Jongsl5. Monastery mentor is hard to make work very well -you need additional mana, or a whole slew of phyrexian spells (and the life to survive).
I think in both Esper Delve and Esper Confidant, Pack Rat is a great card. Low CMC for Confidant, and great ability to flood the board. Flashback and jace/snapcaster/lingering souls are all awesome. Painful truths too, since you'll only need to cast it once a game anyway so Jace/snapping it is great, same for sphinx's rev.
If you lack counters you could play more discard, or play spell pierce and/or stubborn denial (great with tasi/gurmag/pack rat)
I've played around with that and it's great fun. Discarding lingering souls to pack rat is delicious.
Hi I run a deck that is very similar to yours. I think you are going to want to find space for thought scour to get that sweet T2 tasigur. Also Sorin solemn Visitor does overtime in this deck. The main weakness is that you'll run out of cards. I run 4 gitaxian probes too for the mentor.
Including Liliana of the veil, however counterproductive it might seem, is freaking great. - +1 lingering souls is losing only half a card.
Get a big draw spell too like Sphinx's reveation or Painful truths for Jace to flashback so you can refuel. I feel that is fine as a 1-of.