How does everyone get such sharp images…?
Remember, everyone gets lots and lots of blurry ones, too. You only ever see other people’s best ones! You have some great work there, keep it up.
Here’s a great blog post from lenspiration on the topic of tack sharpness.
Make sure your lenses are perfectly clean. Even an apparently small smudge, or a virtually invisible coat of dirt, can affect image quality.
No, shooting in Jpg vs RAW doesn’t directly affect image sharpness, thought it might affect smooth textures slightly (in extreme cases). RAW gives you more power over the colours in your pictures when editing them.
Your example pictures are resized to 2000 px long-edge. I wouldn’t dare give an opinion without seeing the original picture.
For your last question, use the Golden Rule. Don’t post 8 pictures when 2 would do. But if you need to post three or four, like you did this time, you’re fine just putting them in at the same time; it won’t break the website.
Yes, as @musicgal recommended, the Foundations of Photography course, though it might take some resources and effort, could be a lot of help in answering this kind of question.
I hope that helped.