You have to go with what you like to eat - potatoes take a lot of room, and I'm meant to be watching my carbs!! although the rest of the family love them. I grew perpetual spinach in my first year, but nobody else wanted to eat much of it, so I dug it all up. If you are doing carrots, do what you can to avoid carrot fly. I didn't have it in my first year, but got it the following year, and they can live on in the soil, so I have had to rotate where they go. Would have been more sensible to take precautions not to get it in the first place, but I was over confident after the first year's successful crop! It's so exciting though. My husband took very little interest in my raised bed making at first, but once he started going out and helping himself to free veg, I had the last laugh.