From all I have heard or seen, herbs appear to do well in all parts of the UK, I don't think you'd have any trouble. Just place the box where you would get the maximum amount of sun and make sure you feed your plants (preferably an organic fertilizer or even natural fertilizers). Combining a fairly rainy climate with a raised box means a lot of the nutrients will leech from the soil, so you'll have to do supplemental feeding.
That is NOT a stupid question. I killed a lot of herb plants before I figured out harvesting by trial and error. Some herbs are unkillable. Mint comes to mind. Pinch off as little or as much mint as you like and it will grow back defiantly. Basil I just pinch off the top third or so and the plant just gets bushier. Cut the tops off your chives and the plants are ready to trim again in 2 weeks. I prune my rosemary regularly and only use the tender light green stems for cooking. Whenever I prune it, it produces even more of those tender green stems. Cilantro ( you may know it as the coriander plant) does not grow back but I always succession plant it (a few seeds today, a few more next week, etc.) so there is always plenty on hand plus it self-seeds so I have more growing as soon as the seaso0n starts in spring. Hope this helps.
"The odds of my being correct on any given issue are inversely proportionate to the proximity of my wife" BubbaGourmet