I will give you my thoughts, for whatever they may be worth.

Crop rotation - this is mostly done to hinder pests from locating the crops easily every year. In my garden, I wouldn't think it would make any difference, because the entire thing is only 25 ft long. If I wanted the best prevention methods for pests - it would be to use row covers, when possible. You can also plan your planting times to miss the most active period when pests are present. I really can't speak on the subject of diseases, because so far this year - I haven't had any. But, i'd also like to add - if you stop the pests before they get started, most of the diseases won't be present.

How many to plant of each? Simple, how much of each one would your family eat? Also, I would consider which ones are usually only eaten fresh, versus which ones can be frozen/canned. For instance - I'm planning on growing 8 squares of carrots this fall, and if I follow the recommended spacings,(and all germinate) - that's 128 carrots, that can be frozen very well - and used this winter for all of the stews, soups, and other dishes that my family might eat. Now, lettuce would be a different story....as far as I know, it can't be frozen - so, it would have to be eaten as it came in to season. If I were to plant 20 squares of romaine lettuce - there's no way my family could eat it all - that would be 80 HUGE salads. Of course, staggering the plantings could help on this.

Interplanting - your tallest vegetables would need to go on the north side of the garden, and shortest on the south. Squash need alot of room to grow, and carrots, radishes do not. If you plant a squash next to small items, the squash will completely overtake the little plants, and they won't receive as much sunlight.

Anyway, I hope this is of some help to you. Feel free to ask more questions, if needed - we are all here to help.

EG