I probably would if anyone ever did anything for me. Or right after they did it I'd be like, "hey, what's your number?" and then I'd text them "thank u :)" while I was standing next to them. And then I would immediately send another text that said, "sorry, I'm shy lol xD" then I would send another text before they could even think of replying that said, "so what cha up to? I'm just at work. :)"

No

It's not always an email - if we spoke in person I say it in person, I don't go back to my laptop and write an email

Only if said exchange originated in an email.

Sure

Sometimes I do.

Yes but I try to keep it generally short and sweet so as not to come across as overdoing it