C1: Are you 100% positive? I thought they changed this a while back to count paying 2 life for probe counted as paying mana so you'd only need 2 more trinisphere. You are paying 1 phyrexian mana by paying 2 life but its still 1 mana.
From gitaxian probe rulings I found this:
"As you cast a spell or activate an activated ability with one or more Phyrexian mana symbols in its cost, you choose how to pay for each Phyrexian mana symbol at the same time you would choose modes or choose a value for X."
At EE6 in Baltimore I was discussing this with one of the floor judges and he explained that they consider the 2 life cost like a mode of payment, but whether you pay mana or life you are still paying 1 with regard to trinisphere. So even paying the life trinisphere sees you paying 1 and only taxes 2 more on.
good catch on the flashback. As I was trying to parse these scenarios out in my head I thought of flashback being an alternate cost so it wouldn't apply then completely missed that SCM gives a card flashback. But thanks for the catching the spirit of the question too and a full answer on it.