Cobra question and 401k question

Hello, I recently started my own LLC as a veterinarian and most clinics will pay me as an independent contractor/1099 for my various shifts. I have one hospital that does subtract tax so I'm paid as W-2. Am I still able to open a solo 401k if this is not something they provide?

Also, I am no longer receiving benefits after leaving my previous job and I plan to take advantage of Cobra for my health and dental insurance. Can I write off these payments and deduct them for my LLC?

 

Thank you!