Re: (Spoilers) - New enemy faction hinted at?
When you first visit the Remnant city, if you actually read the fluff, they refer to their enemy, presumably the ones that unleashed the Scourge, as "the opposition." I realize it's pretty generic, but I'm thinking "philosophical opposition," meaning probably the same species as the Jardaan, but philosophically opposed. Especially notable in that the Scourge seems to go after Remnant tech specifically.
As for this mysterious "benefactor," I doubt it's the Illusive Man, simply because his whole schtick was control. If he bankrolled the Andromeda Initiative, he'd have left with it. Whoever the "benefactor" is, it's someone who went with them. You don't invest that kind of capital just to die of old age wondering if it was worth it.