With the amount of time it would take them to get back it's possible there are certain condtions of deep space that the Reapers can manipulate to reach the Milky Way so quickly, the mass relay to the Citadel could purely strategic, as with Sovereign they don't want there invasion to be widely publicised as to draw in every race against them. Sovereign was defeated with a relatively small force compared to what each race actually has, I'm pretty sure that the Destiny Ascension was the only dreadnaught (besides Sovereign) used in the battle and according to a codex there are something like 100, give or take, between the Turians, Salarians, Asari and Humans. The Reapers would have the advantage but there are so many possibilites to defeat them, whether through the combined strength of everything you've gathered over the previous games or by something with more finesse then shooting some missiles in there general direction. The star may be used as a way to destroy at least some portion of the Reaper fleet, they wouldn't have any way of knowing that the star was dieing at all, perhaps Cerberus is even behind this.
It seems that they have been mixing in a few aspects of weather changing and stuff like that throughout ME1 and ME2, such as the side quest in ME1 where you discover that the geth have some ability to manipulate weather (although they were heretic geth tied in with the Reapers so this could still be all there doing) so this may have an impact on ME3.
With the resource thing somebody said that if they have to hybernate to reserve energy so how can they make the distance back to our galaxy? Whos to say that they still don't have massive amounts of resources. Why would they just sit active in space wasting fuel when they have the ability to hybernate?
I very much doubt that TIM has anything to do with the reapers considering everything he has done to prepare for them.
As far as the storyline in ME2 goes I believe there will be alot of underlying points that will contribute to ME3, the recruitment and survival of different team members may change how you can complete tasks or whether you can complete them at all, along with there loyalty, for example if Tali was exiled this may diminish your chances of rallying the Quarians effectively, if you saved the genophage cure with Mordin AND got Grunt into the the Urdnot clan AND they both survived this may affect your chances of recruiting the Krogans effectively, even Wrex surviving will add to this.
In my opinion you may end up recruiting the Rachni, Geth, Krogan, Cerberus, the Council races (they still don't believe you) and others I may have forgotten all due to choices in you have made in previous games. The Collector technology can also influence along with the strength of each of these forces.
I know I have been rambling for a bit so I'll stop now but I think there are far to many possibilites to just right off ME2's story line or pick apart every so called holes in the story until we see what they finish off with.
