Your questions aren't terribly clear. I shall try to answer the general gist of what you seem to be asking.Dragonbums said:
The game starts upon or shortly after the arcs arrive in Andromeda. (There might be some prologue stuff regarding their departure but the game proper takes place entirely in Andromeda.)
It is presumed that it's an attempt at a Noah's Arc plan. Send a bunch of people to colonize Andromeda so if the Reapers wipe out everyone in the Milky Way then at the least the various species won't be extinct. There is a single line of dialogue in ME3 that supports this, in which the Asari Councillor says, "There are preparations to make, the continuity of civilization to consider."
There is no indication that the Reapers are concerned with Andromeda in the slightest. They're only ever considered as being a Milky Way thing. Granted, there's no specific reason to believe they aren't reaping it up in Andromeda. I can basically guarantee they won't show up though, after the ME3 ending nobody at Bioware is going to want to touch the word "reaper" with a ten foot pole.
However, as far as I'm aware there has never been a specific confirmation in any of the material or by any of the developers that the arcs were made with the intention of Noah-ing the Reaper invasion. It's just been assumed by the audience because it kinda makes sense. In fact, one the Andromeda Initiative videos says the project was "launched" the year before the invasion. That could mean they literally launched off into dark space before the Reapers showed up or it could mean they began construction that year, then got a whole lot more motivated when the Reapers came a-reapin'.
Bottom line is that the whole Andromeda premise is Bioware trying to put as much distance as possible between their new game and That Ending. I wouldn't be surprised if they say the arcs left the Milky Way before the Reaper war started and nobody in the game ever mentions reapers at all. Which would make sense since the reapers weren't widely believed in basically right up until they set about ruining everybody's shit. However, that would just lead to more questions. For instance, would that mean that any Krogan coming along are still nigh-infertile due to the Genephage? Why are they undergoing a massive effort to leave a supposedly safe and still massive and relatively unexplored Milky Way?
Bottom-bottom line is that it's a retcon of sorts. They're retroactively sticking a major development into the setting that was never mentioned in the previous games. That's going to inevitably result in some narrative awkwardness.
