How to say "love” in Japanese?

I have made good friends with a few Japanese overseas students, and they always laughed at me saying Konnichiwa whenever we meet as they think it is too formal or classy. I want to know if there is a casual Japanese word for “Hey” or “Yo” that you can use when greeting a close friend. If possible, please teach me the male version of “Hey” or “Yo”.

Question: I have just joined a baking class and there is another Japanese student who has just joined as well. Since both of us are new, I thought I would greet her in Japanese. How do Japanese people say “Hi” or “Hello” when they see each other?

Question: My Japanese friend called me the other day. I thought I would try answering the call in Japanese, but I don’t know the word for “Hello”. Is there an equivalent for “Hello” in Japanese?

Question: I was on an exchange program to Japan and was staying with a host family. They were very nice, but their seven-year-old son was a handful. We were watching TV in the living room when the boy suddenly came over and started pulling my hair. I thought it was a one-off incident and was going to ignore it, but he continued pulling it harder. I was getting annoyed and wanted to say “Stop it” but I don’t know what’s the Japanese word for it.

Question: My son brought his Japanese girlfriend home for dinner. After dinner, they went out for a walk. I thought I would try to be friendly to the girlfriend by saying “welcome home” when they come back. How should I say this in Japanese?

Question: We were in the middle of a group discussion, but my Japanese friend had to go for her consultation with her lecturer. We were going to continue our discussion again later in the afternoon. How do I say “See you later” in Japanese?

Question: I’m typing a message to my Japanese friend and I want to add lol at the end of the message. Is there a Japanese equivalent for “lol”?

Question: We are pitching for our next project with a client and my colleagues are going to deliver the final presentation. I want to wish them “good luck” in their presentation but I’m not sure how to say it in Japanese. What’s “good luck” in Japanese?

Question: Someone rang my doorbell but I can’t see who is at the door as I do not have a door viewer. How do I say “who is it” in Japanese?