Go to the Diet Section and look at the sticky called "Plant ID". There are lots of them there. You can also take pics of your local weeds and we can tryo to help you ID them. Or you can take samples to a local nursery for ID help.
I like to feed Mazuri once or twice a week. As much as they want. Some people never feed it. Some people feed it nearly every day.
Its your choice. There is no right or wrong necessarily. My preference is twice a week. Others might have a different preference.
I occasionally use spring mix or other grocery store greens, but I try to use mostly grass, weeds, leaves and cactus. You could use some scissors and trim some nice fresh green grass to mix in with that spring mix. Chop it up really fine and it will stick to pre-wetted spring mix.