IMO , if you have erosive soils, then plant a cover crop with the alfalfa, but don't take a small grain to harvest.  To risky.  The grain can easily lodge, and you can get volunteer grain from combining it.  Most agree that oats are the most forgiving of cover crops for alfalfa.  HERE, we like our round-up ready alfalfa.  We plant 1.5 or 2 bushel of oats, and either spray and kill the oats when it is 8 inches tall, or take the oats for forage, wait a week, and spray round-up and an insecticide for leaf hoppers, and usually get at least one more crop, but usually 2 additional crops, and still have some regrowth before winter.  

If the crop that precedes the seeding is soybeans, then a good no til drill, like a JD 750 style will give you an excellent stand of alfalfa and no erosion.  

A neutral pH, and adequate P and K are very important.  

Depending on how many acres you are going to seed, there are several that can work well.  For large open fields, and large acreages, a terragator type airflo can do a great job, but most recommend making 2 passes to insure an even spread, but for smaller acreages, any grain drill with a small seed box, or a brillion type seeder work well.  Plenty of people would recommend using a roller of some type before seeding, and or after, but it is not vital, but having a firm seedbed is.  A couple passes with a drag can work just as well.   Yes 15 - 20 pounds of seed and a firm fine seedbed will normally get you a great stand .  Be certain to get a very winterhardy variety for northern minnesota.  

Good luck