Marigolds love the heat and are my favorite for hot, dry spots in the garden.

Yes, a few herbs help with that. Citronella plant is the best one. You can crush the leaves and make a spray by soaking them in water. Drain off the leaves and use the spray.

Looks like thyme on the left and golden oregano on the right. Lucky you! The sniff test (pick the herb, crush the leaf, sniff it) can also help you -- you can compare the smell to what's in a spice cabinet.

The one that's suited to the weeds. Seriously. Each product is made to target different weeds at different stages. For example, pre-emergents kill prevent weed seeds from growing. Round Up works very well on most weeds.

Unless they are fire ants, leave them alone. Ants harm no one. Fire ants, on the other hand, should be treated with a commercial product to get rid of them, especially if you have children as the stings hurt!

The mold actually spreads from beetles that bite the leaves so the key is to control the beetles. Use special barrier cloths, available from the garden center, to keep the bugs out!

It's really important to manage them not just when you see the damage they cause, but at all stages of their life. As Susan says, you need to manage the grubs. Here's a good pamphlet from the USDA which explains how to manage them: https://www.aphis.usda.gov/plant_health/plant_pest_info/jb/downloads/JBhandbook.pdf

I wrote an article on this which might be helpful: https://homegardenjoy.com/site/2015/07/hydrangea-not-blooming.html

Rich loam is the best. You can create it using compost added to almost any soil.

I've never known them to bite and they are beneficial insects!

Beer! Yes, beer. Place an inch of beer in a pie plate. Slugs crawl in to drink the beer and drown. You can also just tip the bottle on the side with some beer in it; same result, dead slugs. Copper tape, which you can buy from a garden center, will repel them instead of killing slugs.

You can brace them and/or dig a little bit into the soil to anchor them.