I have been 'shoving it in where there is space' for years. And I teach horticulture so crack on with that method IMHO. I only rotate potatoes around my allotment and I leave any that grow from old tubers as freebies.
Fruit - I have grapes and spiky stuff [wineberry mainly] that is wired - the rest is left to it's own devices. My rasps - I have 18 in two rows 18 inches apart with a path around them, and because I don't tie them into anything I can grow them closer together and then just walk in amongst them to harvest. I underplanted with strawbs and chives to make the best use of space and to add some companion planting, and also there are marigolds and limanthes scattered around. I have a gooseberry at on end, underplanted with more chives and strawbs, and two blueberries and a chokeberry at the other, also underplanted with chives and strawbs. So in one 20ft x 3ft area, there are 18 rasps, about 50 strawbs, a gooseberry, 2 blueberries and a chokeberry and the only thing I have to do is mulch in autumn and prune in winter. And bung a net over the gooseberry in the week preceding harvest or the pesky birds will have the lot overnight.
Raised beds, they don't have to be raised immediately. Just keep adding organic matter and over the years they will raise up to the level of the wood. I would recommend however a slight angle to them.
If you make the sides of the beds lower on the most southerly side, and higher on the north side, and angle the soil low at south end and high at north end, for every degree of slope you gain an extra [don't quote me on the exact figures] an extra ten minutes of effective sunlight. So I always recommend that people angle their beds to the sun. This warms the soil faster, and helps the soil to catch more rays in the winter.
All my beds are sloped to the sun, you just get a better return on investment.
Companion planting - is one of the keystones of organic gardening. Also - steer clear of growing the same things all together. And interplanting - so by the time the faster things have been eaten, the medium time things are just coming up for harvest and once they are gone, the slower things are then welcome to have the space. EG - brussels take 9 months, so 50cm away put a courgette, and in between pop some rocket and lettuce with a few radishes. The radishes come out first, and then the rocket and lettuce. Then the courgette crops until Sept/Oct, by which time the brussels needs the full space and will sit there all winter. If you put another brussels 50cm the other side of the courgettes - there you have a good foundation for your winter beds. Then once the courgette is out - mulch the ground around the brussels.
Also, if you are using beds, don't waste the space by plonking a courgette or squash right in the middle of a bed - put it near the corner and let it trail on the path not the soil. Maximises your soil space.