Welcome to the site! It's great that you rescued this betta from your friend!
1) Males often make bubble nests. There's debate as to whether they make them because they're happy, or if it's just a normal process for adult males seeking to attract a mate. Some fish make them more frequently than others. Some make more elaborate ones than others. And some don't make them at all.
As for when you had the filter, it's possible that the current made it difficult for him to build a nest. They tend to fall apart when there's water movement. (I always feel badly when I clean my guy's tank, and it ruins his nest!)
2) Two of my bettas LOVE lying on top of their plants! They'll sleep in them, or just hang out. I made a betta 'hammock' out of a silk leaf for my female, and she sleeps in it every night.
Two of my fish like to swim near the top. The other likes to be near the bottom. All three have identical tanks. So there may be a bit of 'personal preference' involved.
As for the water temp, some fish seem like it warmer than others. One of my guys seems to prefer cooler temps than the other two.
Not sure about the LED light. I don't have one of those.
3) All three of my guys do a 'happy dance' when they see me. So I'm thinking that your guy is happy to see you too! But.... to be honest, they probably associate us with FOOD! (I can just picture my guys thinking, "Ooo! Breakfast time!"
) And they definitely love to eat.