I think the best approach for the raised bed layout is to group plants by their watering needs rather than by size. Tomatoes and peppers do well together since they both need consistent moisture, while herbs like rosemary and thyme prefer drier soil. I usually put those along the edges so they don't get overwatered. For soil, I mix in compost a few weeks before planting and add a slow-release organic fertilizer. Mulching with straw helps retain moisture and keeps weeds down. I also rotate where I put the nightshades each year to prevent disease buildup in the soil.