Mull sth over, think sth over, chew sth over, think sth through, think abt sth

Hello there,

I've just sent an email to a guitar seller and wanted to ask you for two things. One, could you please give it a quick look and tell me if there are any non-native sounding sentences or errors that I could avoid in the future.

Here's the email:

Hi, Bob

I have to mull it over. It's a great guitar, no doubt, and a real rare gem. Would love to own it, but I have to admit that I'm currently without a stable source of income, so I really need to watch my expenses. Still, I have some money stashed for special occasions and this might be one of them. I've got to think it over.

Best,

Kat

P.S. I have a friend living in Maryland. Perhaps sending the guitar to him would reduce the costs significantly. I need to get in touch with him and ask if it would be possible. Last time we talked he was changing apartments. I'll see if he could help.

Also, I'm wondering if there is any difference between

to mull sth over

to chew sth over

to think sth over

to think about sth

to think sth through

In this case, I told the seller that I need to mull over the decision of buying his guitar.

Thank you.