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'?)

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.

1. Yes, the sentence "He is so kind to help me" is correct. Other expressions that can be used to convey a similar meaning include:

- He is very helpful.
- He goes out of his way to assist me.
- He is always ready to lend a hand.

2. Both sentences are correct, but they slightly differ in meaning:
- "I don't spend a lot of money in buying things" implies that you don't spend a lot of money while you are physically engaged in the act of buying.
- "I don't spend a lot of money on buying things" implies that you don't spend a lot of money when it comes to the overall process of purchasing things.

In this scenario, it is more common to use "on" before "buying" as it captures the broader spending concept.

3. The phrase "get going" means to start an action, leave a place, or begin a journey. It can also be used to imply that one needs to start or resume an activity without delay. Other expressions that convey a similar meaning include:
- It's time to leave.
- I should start now.
- I need to get moving.

4. The phrase "move along" means to leave a particular place or situation. It is often used to politely decline an invitation to stay longer and indicates that it is time for someone to depart. Other expressions that convey a similar meaning include:
- I should be on my way.
- It's time for me to go.
- I need to continue my journey.