Q. Will I benefit from different tire size or type?

I have 700 x 35 tires on my hybrid bike, and I've recently learned
that I can change the 35 (width?) to a different size, ie. 32, 28 etc.
Question is, do I want to? I ride exclusively on pavement in a city,
so I'd like to maximize tire efficiency for this type of driving.

- First of all, will it work to put different width tires on my
hybrid/city bike, or is there an issue with narrower widths coming off
the rim, etc.?

- Secondly, is there an advantage to using a different tire size if I
can, or should I assume the original 700 x 35 tire size was already
designed ideally for city driving?

- Lastly, I read expert testimonials that said slick tires are best
for pavement riding, cornering, wet driving, traction and have less
rolling resistance, basically because more rubber contacts the road. I
was looking to buy the Michelin Transworld City, but its not a pure
bald slick, it has fairly deep recesses, presumably to siphon off
water (which I read isn't necessary for bike tires, and that this
system doesn't work better than slicks). So my question is, would I be
better off driving in my city with a pure bald slick, such as the
Avocet Road 20, instead of the Michelin Transworld City? Or is it even
better to use DIFFERENT TIRES for the front and back? Any commonly
known disadvantages to going with pure bald untreaded slicks on
pavement, such as premature tire wear, as compared against tires with
a tread?