Just my opinion...

1. Johnny's Selected Seeds- but they may be a tad expensive.
2. The veggies you picked are not really high maintainance. They should be ok. Carrots do need a loose soil, corn shold be planted in a square for best pollenation and only the corn would like that much fertilizer.
3.Wait for the soil to dry before working it. General rule here is to roll up a golf ball size wad and if you poke it with your finger it should break apart. If not, it's too wet.
4.Put the cow manure in the compost and the rabbit manure on the garden. Is it really cow manure or a composted variety from the store? Do not put fresh cow manure on a growing garden, especially lettuce or root crops.
5. Varies with the pest.

tj

Much of Southwest Michigan has sand for soil, although there are pockest of thick clay, and if what you have is that sand you need to add lots of organic matter so that sand will be able to hold nutrients and moisture in that soil since sand tends to drain really well. However, if you have clay you will also need to add lots of organic matter to seperate the clay soil particles so these same nutrients and moisture will be able to move through that clay to the plant roots that will also need that organic matter to move around in that clay.
Contact your local office of the Michigan State University USDA Cooperative Extension Service about having a good, reliable soil test done so you know what your soils pH is and what, if anything, needs to be done to correct that as well as the base nutrient levels. When your soil is workable dig in with these simple soil tests to see what you have,
1) Structure. From that soil sample put enough of the rest to make a 4 inch level in a clear 1 quart jar, with a tight fitting lid. Fill that jar with water and replace the lid, tightly. Shake the jar vigorously and then let it stand for 24 hours. Your soil will settle out according to soil particle size and weight. A good loam will have about 1-3/4 inch (about 45%) of sand on the bottom. about 1 inch (about 25%) of silt next, about 1 inch (25%) of clay above that, and about 1/4 inch (about 5%) of organic matter on the top.

2) Drainage. Dig a hole 1 foot square and 1 foot deep and fill that with water. After that water drains away refill the hole with more water and time how long it takes that to drain away. Anything less than 2 hours and your soil drains too quickly and needs more organic matter to slow that drainage down. Anything over 6 hours and the soil drains too slowly and needs lots of organic matter to speed it up.

3) Tilth. Take a handful of your slightly damp soil and squeeze it tightly. When the pressure is released the soil should hold together in that clump, but when poked with a finger that clump should fall apart.

4) Smell. What does your soil smell like? A pleasant, rich earthy odor? Putrid, offensive, repugnant odor? The more organic matter in your soil the more active the soil bacteria will be and the nicer you soil will smell.

5) Life. How many earthworms per shovel full were there? 5 or more indicates a pretty healthy soil. Fewer than 5, according to the Natural Resources Conservation Service, indicates a soil that is not healthy.
and what you need to do to make your soil into a good, healthy soil that will grow strong and healthy plants.
Manure should not be added to your garden until after it has been properly composted due to the potential for disease pathogens that are present in all manures. The current issue of Organic Gardening magazine has an article that states manures should not be added to any garden unless it has been composted or aged 12 months, which would be a major waste of the nutrients in that manure.

Here is a link that might be useful: MSU CES