I very much doubt you would have problems putting 27 x 1-1/4" tires on those rims.

Cheng Shin tires are really not bad unless you're looking for high performance. Months in the sun will cause them to discolor and start to break down, but that's not good for any tire.

Gum wall means the side of the tires is not black, but rather a color that is like gum rubber. It is also a different compound than the tread portion of the tire. Gum walls tend to be a little more supple than all black tires, which many people think provides a nicer ride.