Quick Grammar Questions

Hello,

I just need some clarification on a couple of sentences. Thanks in advance for your help!

1. "Stealing ideas from one person is plagiarism. Stealing from many is research." Is this grammatically correct?

2. Are either of the following sentences grammatically correct?

"A tenant may get frustrated by a landlord's behaviors during your time staying in the rented apartment."
"A tenant may get frustrated by a landlord's behaviors during his or her time staying in the rented apartment."

3. Are either of the following sentences grammatically correct? I have a feeling the second one is, but I'm not 100% sure on the first one.

"If you need clothing that is versatile, and dependable, then look no further, because we have the lowest prices around."
"If you need clothing that is versatile and dependable, then look no further because we have the lowest prices around."

Thanks again!