Sounds like you have a beautiful landscape going there! Heuchera's can't take the southern summers in your region and thus are not recommended for your zone. Tithonia is not normally difficult to germinate. Moist soil (don't let it dry out our stay soggy), sunlight and warm conditions are what is needed. Your seeds may not have been good. Try some more in small containers in a bright shady spot. When they germinate move to a morning sun location and then after another week or so plant them out into the garden.
You sound like a gardener who can't wait to get started! But please, one question at a time. We are building our database of answers for other gardeners and can only use single questions. But feel free to post single questions as many times as you like.
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