I’ve got some traditional veg patch and some raised beds. 8’x4′ is good for raised beds. I guess as longs as you like but the critical thing is keep it to 4 ft wide as you can reach in to the middle from both sides so you never have to walk on the soil of the bed like you would on a normal veg patch. Saves loads of digging if you don’t need to compact the soil.
Go for it, keep it simple and grow stuff that tastes best fresh. I used the raised beds for salad stuff and French beans etc. keep the spuds etc in the normal beds.
A mate of mine asked me to help him put a rabbit fence around a new veg plot. He made it E shape, it was mad, more paths than plot and when I went back a few months later he’d filled it with onions, potatoes, cabbage and turnips or something. All veg that is cheap, stores well and you could buy anywhere….. The gardening thing didn’t last long….