You have the same questions that many of us have had...is the 35-70 on my DX camera really wide enough for what I would like to do? On your D 90, it gives you the equivalent angle of view as a 50-105 on FX. So, if you do interiors or landscapes regularly, and like the sharp-from-front-to-back photos that Bryan Peterson does so well, probably not. The F/2.8 is a marvelous lens, but, in these days of adjustable ISO, the difference between f/2.8 and f/3.5 is rather moot.
I'm not a real wide-angle person, but I do find the wide end useful every now and again; but for an all-round, excellent lens, my DX 18-70mm AF S is a good one. I think the newer 24-85mm lens would probably do as well.
Lens makers are involved in the art of the "possible"...how to design a lens at a price point that most of us mere mortals can afford. That means there will be some distortion somewhere...guaranteed! But, Who notices? Almost nobody!
Anyhow, the D 90 has a distortion control program built in...Retouch menu...the little brush icon on the left side of the screen then scroll to Distortion control, right under STRAIGHTEN. I think the default is ON.
Ken Rockwell says it doesn't do much,(enough?) but IMO it will correct a lot of what we mostly don't notice anyway, so I leave mine on. If you are a good Photoshop person, there is also a feature there to remove lens aberration.
My idea of a good, do everything kit would be the 18-55,"Kit" lens, or the 18-70, plus a Macro, and the 70-300 VR, or...and I'm dreaming,here, the 70-200 F/4. O My, Yes!