On the slicks question--

My main reason to prefer them is that they're less likely to slide out on pavement, since they have a larger contact patch with the smooth surface. The difference in speed, although real, is minimal. But you really will notice the difference in gription. In fact, IMO one reason that slicks are faster is because they are more secure, so you don't have to slow down as much on turns and curves.

The down side: Obviously they're less good on riding surfaces that are not smooth. Also, you're likely to have flats more often.

You can get decent 26 X 1.75 slicks for $10 or $15 at just about any bike shop or online. For $20 you can buy very nice ones-- 1.5 inch, 85 psi, and good sidewalls. You can use the same 2 inch inner tubes, but when you buy a replacement tube get it in the smaller size.