The front page of this website will tell you recommended sizes for cages, a 2x3 C&C cage (roughly 28 inches by 42 inches) is commonly accepted as the minimum size of a cage for a guinea pig. Also, rat cages tend to add height as additional room which doesn't work as well for guinea pigs, they need more open space to run and additional levels should be seen more as a bonus rather than compromising on the size of the base cage. Temporarily, I suppose that cage could work until you can find/build a more suitable cage, but it is a very tight squeeze and I would really suggest giving as much floor time as possible.
The wire mesh is more than a preference problem, guinea pigs can easily have their feet slip between the bars and can really do some serious damage. If you have to use the cage temporarily I would put down a decent layer of fleece to avoid any accidents.