Hi Sam. Even before you start planting your first raised bed, you can sow some oriental salad greens in a bucket , tub or big pot. I only started to grow them this year but have found them excellent. They start to crop in just a few weeks and suddenly you have enough for a plateful of delicious salad every day.
I have not used raised beds, but in any system you need to have some sort of rotation of crop types. This helps to prevent the build-up of soil-borne diseases specific to each crop type. The usual way is to keep all the legumes together as they return nitrogen to the soil. Potatoes are great for clearing the ground and they need plenty of muck dug in, which then leaves that plot ready for something like roots the following year. Roots like rich soil but they hate fresh manure, which makes them fork, so if you plant them after potatoes there is still plenty of nutrition in the soil. Brassicas are also heavy feeders and suffer from two major problems - club root and cabbage root fly, so they need to be rotated too. The alliums ( garlic, onions, shallots and leeks) suffer from various soil borne diseases, so you need to fit them into the system as well
Salads and so on fit in around the others and permanent plants such as rhubarb and globe artichokes need a separate bed. Strawberries can be fitted into the rotation system as they are replaced every three years, on a rolling system (ie you replace one third of your plants each year).
This is just touching on rotation. The best thing is to buy a good vegetable gardening book (you will be spoilt for choice) so you can plan what you want to put where and get it right from the start. It will also keep you right about when to sow and harvest what, and what you can sow direct and what needs to be started off indoors.
I keep meaning to ask people why they use the raised bed system. What has made you decide to go that way? Vegetables grow perfectly happily in the ground without all the time, money and hard work of making raised beds, which harbour slugs and weed roots in the edges, and need extra watering in drought conditions. They also make it very easy to jam your fingers between the fork handle and the edge of the bed when you're lifting tatties. They are very useful where the soil is thin or very poorly drained, or for people who are disabled or elderly and need to work at a certain height. I work my ground with a rotavator (being of the slightly elderly type so digging is difficult), then I use weed suppressing fabric to make flat beds with paths between for some crops and I grow the rest in ordinary rows. Much more flexible.