... sticking to the first season takes place sometime pre- avengers and then continues from there SO that the timelines can be matched up and these SHIELD agents brought into AVENGERS 2 on a more linear narrative note. Having it pre does NOT take the stakes away because THESE agents should have stakes all of their own. Their lives don't rise and fall on Tony Stark. Hell, just look at any series based in a past crucial time period or period films- just because you know the news headlines, does NOT mean you know the people.
As for Coulson coming back? Wishful thinking for the fans. Reviving Coulson from the dead... kinda sounds... cheap and character-wise something they'd give Thor more for character sake (Tony wasn't there when he got killed nor by his brother, it would make more sense emotionally if Thor saved him if he was to return). So, then, as said TECHNICAL-wise and the way the two lineup, for the two to lineup you'd need to do SOMETHING and setting part of the series pre makes the most sense. Lining the two up so that the show doesn't go beyond the films would be a logistical nightmare, not really to get them lined up- but not to create any glaring plot holes from the series into the films and vice versa.
And if someone brings up stakes again. Argo ring any bells as a more recent example? And that IS the story. Focusing on SHIELD they have stakes and missions and everything all their own. Now... I forgot the timeline I lined up earlier, but I think (may be wrong) for the two to match up the first OR first and part of the second season would be pre-Avengers.