You will have erosion problems only if you leave the ground bare. Establishing a prairie is usually done with a cover crop of annual rye or oats to keep the soil covered while waiting for the prairie plants seeds to germinate, so erosion should not be a problem.

The seed catologue from Prairie Moon Nursery has detailed instructions on starting a meadow. See the link below

Here is a link that might be useful: Prairie Moon

You could use a cover crop or you could use an erosion control blanket. Its a netted matt, that acts as a mulch that holds the soil and seed in place until the vegetation gets established. Evenutally the matt decomposes.

http://www.nagreen.com/products/SC150.html

I used an erosion control blanket from North American Green and it worked well on my first try. Some blankets are completely degradable and some are not. For wild life and human safety I tend to prefer a blanket that is completely degradable in some manner so that no one gets tangled in left over netting years later. Some blankets are biodegradable but with a plastic netting mixed in that is photodegradable. With either of those options, you should not have to remove any of the blanket once installed since it all disappears within a few years. The blanket is put over the seed. You can also cut holes in the blanket to install previously grown plants. The top edge (and sometimes the bottom edge) is buried and the whole thing is pegged in at regular intervals on the blanket. Make sure to order a lot of pegs with the blanket. The blankets often have the spots for the pegs marked on them so you don't have to guess. During the winter and before I planted the native seed and installed the blanket I held the slope together with cereal rye which I killed before doing the native seeding and blanketing.