Welcome back to biking! You got a nice bike at an even nicer price. While bigger tires can certainly be more comfortable in some conditions they may not be needed. Where do you think most of your riding will be. Paved path? Proper inflation front and rear is very important to comfort, maintaining control and traction. The pdf below gives the correct pressure front and rear for a variety of tire sizes and rider/bike weights. A more aggressively treaded tire could actually be harder pedaling while not improving traction.

http://www.bikequarterly.com/images/TireDrop.pdf