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If they are in the ground, an average of 2" (5cm) rainfall or manual watering is recommended. If you find that you are in drought conditions, you can bump this up to 3-4" (8-10cm) a week. Water does not need to be given daily, and if they are in the ground, it is acually healthier for them to be watered only 2-3 times a week.

If they are in containers, water daily until water runs out from the bottom for the container.

What about using neem oil? It's a good organic 3 in 1. This article will explain it better than I can: https://www.gardeningknowhow.com/problems/pests/neem-oil-uses.htm

By the time the plants are 4-6 inches long, the cucumber will start to trail. The sunflower will stand upright. Hope this helps.

These articles should help you: https://www.gardeningknowhow.com/ornamental/flowers/sunflower/planting-sunflowers.htm
https://www.gardeningknowhow.com/ornamental/flowers/sunflower/growing-sunflowers-in-your-garden.htm

I would recommend not using a glass dome and full, direct sunlight together. The combination of the two would result in elevated temperatures under the dome that would likely kill the seeds. A glass dome in bright indirect light would be helpful, but not necessary to germination of either plant. Really, it is not so much about the light - most plants unless specified on the package do not need light to germinate. It is about the humidity and the heat. The glass dome would provide elevated levels of humidity and in indirect light would help increase the heat some.