Never grown cucumbers so can't help with that. As for the timing of the aubergines, I don't follow the too early logic? If you were hoping to plant them out, I'd agree but I assume you'll be growing them inside? I know that's my plan and I've got them in early (along with the peppers) to maximise the growing season. They take ages to ripen and I tried to grow them outside (from an established plant) in Switzerland where the summers are much hotter and they never ripened. So my logic is that I need to get them in early so that they make the most of the summer to ripen fruit rather than planting in May and spending most of the summer growing the plant. I'll not be seeding pumpkins, courgettes and squashes until later because they will go outside and I need to time it right re.frost.
H