The best way to buy is the new E Z Streets which is 100% compatible with Super Streets except the color is different. Buy from an online vender rather then from Bachmann's website as you may save 40% or more buying from an online vender.
The WBB set with an E Z Streets car comes with 21 inch curves, a couple of 10 straights, 4 straight adapter tracks(2.5 inch), a car, the Plasticville Turnpike building and a power supply. The power supply from Bachmann in the E Z Streets set will power a Plymouth switcher set, diesel engine with 6 small freight cars. The Plasticville Turnpike looks nice but is limited to 1 track through the main area(between booths) and is only tall enough for Super Streets or E Z Streets vehicle to go under it.
There are 2 sizes in E Z Streets curves; 16 inch(D-16) and 21 inch (D-21). The regular straights come in 5 inch & 10 inch sections. Track adapter straights or curve to curve straights come in 2 & a half inch sections; curve to curve allows you to use the 2.5 inch straight between 2 curved sections, the 2.5 inch straight to curve is used for coming off a curved section to transition to a straight track. You can buy the track by pieces or in a set.
As for the Peter Witt trolley working with E Z Streets or Super Streets I have no idea if it will do the 21 inch curve or not.
K-Line's Plymouth switcher, and small hand cars will run on Super Streets or E Z Streets. I have an MTH Septa trolley that works on 16 inch Super Streets curves. Any K-Line Super Street vehicle and most WBB E Z Street vehicles should be able to go through the 16 inch curves. Maybe a small BL-2 diesel will work on E Z Streets. A lot of times it is trial & error as to what will work on E Z Streets track.
Installation tips for either E Z Streets or Super Streets; pop the manhole covers out with a paper clip(unbend it first) from the topside or use a small track pin and pop it out from the bottom. Also a # 4 phillips head screw about half inch long(flat top or tapered top) works best to attach the track to a layout. Power wires can be attached to the 10 inch straight(both hot & neutral) or just the neutral can be attached to a curved section.
Lee Fritz