I've driven a few of my previous mustangs in the snow... with and without a sandbag in the back just takes tons of patiences and discipline is all.. I wouldn't suggest it is a hell of a rush at times
About the gearing.. Since it's your daily driver I wouldn't really go beyond the 3.55 mark because with the 3.73's I never liked hitting the hight way mpg tanked and the rpms would be soo high i'd have to drive in the slow lane so it was bare able. I'd say if your plans involved hititng the track allot or a few times a week or month then maybe you could get good use out of the 3.73s and higher ratios but if your cruising or using it to get to point a to point be over and over don't do it. On our turbo gt we actually had to remove the 3.73 and put in some 3.27s to get the most out of her in the 1/4 mile so there is a such thing as over gearing a car.
I'd personally get someone to weld up you some subframes.. ones with the cross brace that ties into the seat bolts (if not your seats will eventually rip the floor pan), also the subframes welded in will help the car feel more solid as well. From there do shortie headers, x pipe and catback of choice and please get the lx style tips so it goes with the cobra rear valence.
With all that the car will sound good and feel better and aside from that stuff things start to get expensive so sit down and figure out what your actual overall goal for the car is and how much you have to fund that goal. Then you can figure out exactly how serious you want to get because slapping a turbo kit on a stock block car can turn into hell... especially if it's not properly tuned your stock block will crumble