Kitava's Thirst + Channeling question

No. Spending 50 mana, then spending 50 mana, is not the same as spending 100 mana - each spending event is independent.

If you can raise the cost of a channelled skill above 100, it will trigger on the initial cost, but not each time you spend that much to maintain the channel, because it only triggers when spending mana to use the skill, not to maintain an already-used skill.