oh oh oh oh oh - I can help here!!
I can't help with much, but this, I can help with!!
Don't use ACR to sharpen that's one thing I have learnt, turn that off (or dial it back for starters)
when you bring it into Photoshop (I'm assuming you use it sorry) I use this method for sharpening images if they need it:
1: duplicate your image on another layer (ctrl J) and set it to overlay
2: Go: (I'm working from memory here) Filters/Other/High Pass - and set it between 1 and 3 (depending on the image) - any higher than 3 you get that horrible obviously over sharp black and white lines thing going on.
...and you're done.
If you're keen, you can also mask out areas that are too sharp, but that almost never happens for me.
Now - important note here!!!
If you're resizing for web use - make sure you have Bicubic Sharper selected in the (I think) 'Resample Image' drop box when you have the resize image dialog box up.
You can set that as the default if you go - and here I'm guessing again:
Preferences/General - select Image Interpolation and select Bicubic sharper.
et voila!
***DISCALIMER*** this will not make fuzzy images look good.
I use a 24-70 f2.8 and I like it a lot - to answer question 2, but again it depends on the light and my stability at the time.
I hope this helps!!
Edit:/// AWWWWwwww crap - Jess beat me to it . . . . must learn to type less . . . . .