I am selling some of my stuff because I do not have time to use them. I want to say something like:
1) "I am selling them because I no longer have time to use them."
2) "I am selling them because I no longer have time to use them due to new work commitments."
Q1) Are the above sentences 1), 2) correct?
Q2) Please suggest me more reasons that can support the reason why I do not have time.
Stuff is singular.
You're selling some of your stuff because you no longer have time to use it.
You're selling some of your things because you no longer have time to use them.
(How can we suggest why you don't have time to enjoy your possessions? We don't know what's going on in your life!)
I'm not a teacher, but I write for a living. Please don't ask me about 2nd conditionals, but I'm a safe bet for what reads well in (American) English.
"Stuff" takes the singular for this BrE speaker too.
I have stuff.
Where is it?
It's in the garage.
Where's your stuff?
It's still in the car.
As far as the OP's question goes, you can say "I don't have time to use it" but if you really are selling some of your stuff, you don't need to explain why you're selling it. The buyer simply needs to know that whatever it is, it's still in good/working condition and that you're not selling it because it's broken. That is covered by simply saying "I don't need it any more".
Remember - if you don't use correct capitalisation, punctuation and spacing, anything you write will be incorrect.