Question

1. He is so kind to help me.
(Is this correct? What other expressions can we use?)

2. I don't spend a lot of money in buying things.

2-2. I don't spend a lot of money on buying things.
(Which is correct? Which preposition do I have to use before 'buying'?)

3. I should get going.
(What is the meaning of 'get going'? What other expressions can we use?)

4. A: Can you stay a little longer?
B: Sorry, It's about time I move along.
(What is the meaing of 'move along'?)

Answer 1

1 is correct. You could also write, "He is very kind to help me."

2 is somewhat repetitive. Simply this will do: "I don't spend a lot of money."

2-2. <~~same comment as above. You don't need "in buying things" or "on buying things" because that's what "spend" means.

3 means I should leave now or I should go somewhere else now.

4 is OK except for the capital "I" on "it's" (should be lower-case "i" since it's not at the beginning of the sentence. To "move along" means to go somewhere else.