First off, I would take the 3-series because I don't think the 525i is powerful enough, but then I think anything less than 0-60 in about 6 seconds is weak...but that's just me. I know not everybody drives like that
Also, you can get more cool stuff for the same money if you get a 3-series (and a more powerful engine) as opposed to a 5.
That said, the new 5 certainly is sexy, so if you're set on getting one here's what I recommend. If you must get the 525, at least get a manual so that it's a bit faster. I have no idea what the price difference is between 525/530, but I guess it's significant, huh? Now I don't know what you think of the previous 5 series, but something else you may want to think about it spending your money on a one or two year old certified pre-owned BMW. Those are effective brand-new cars anyway, and with the same amount of money as you might cough up for a brand new 525 you could get a more powerful 530i or even 540i through CPO.
As far as bluetooth, your dealer is lying. It is available. I just sat in an E60 last week that had bluetooth.
I can't help you with BMW Assist, I don't know anything about it.
Navigation--I don't have very much experience with BMW nav, but I know that Acura's and Lexus's are the best and BMW is not as intuitive as theirs. It's useable, just not as well-designed.
Snow...one thing I was pleasantly surprised about with BMW. I thought it would be a nightmare to have a rear-drive car in the snow (I live in northern Indiana, close to you), but with BMW's awesome traction and stability system it's really quite easy to control the car. You just have to drive cautiously, of course, but it's entirely manageable.
So, the 5's a great choice, but if I were restricted to the 525 I'd go for a more powerful 3-series. But then if you're not one to drive hard, the 525 could be perfect for you. Good luck, and let us know what you choose!