No.1 to 4. Sencond words are all 존댓말. And of course you can say 생신 축하해요. 5. It means "feel unwell". 6. 힘들어요 means "it's hard" but 힘들어서요 (힘들어 + 그래서요) means "because it's hard". 7. 연세 is also 존댓말. :)

5. What does 편찮다 mean? 아프다 vs 편찮다 (Casual vs Polite) This means "sick or ill so not feeling well" 6. 힘들어요 and 힘들어서요? I know they both mean 'It's hard' but does having a different ending change anything? This is not "Casual vs Polite". 힘들어서요 is like "Because it's hard." and if you go, 힘들었어요, it is like "It was hard"

It's a difference between casual and honorific politeness level. (Casual vs Polite) 1. 생일 Casual 생신 Polite Can I say "생신 축하 해요"? you can say that. anyway, 생신 축하드립니다 is correct in grammar. 2. 있다 and 계시다? (Casual vs Polite) 3. 가다 and 가시다? (Casual vs Polite) 4. 말하다 and 말씀하시다? (Casual vs Polite) 5. What does 편찮다 mean? 아프다 vs 편찮다 (Casual vs Polite) 6. 힘들어요 and 힘들어서요? I know they both mean 'It's hard' but does having a different ending change anything? 7. 나이 and 연세? (Casual vs Polite) Yes, there are honorific nouns. It's like you say 'Your majesty' to the King or Queen Instead of saying 'excuse me'