Try to answer as I understand below:

 1. do all the MA need to pay part B or only MA 0 needs to pay part B ? 

Yes as you need to pay SSA (Social Security Administration), not to provider, SSA will deduct Part B from your Social Security Benifit directly or you pay to Medicare.gov before starting SSB.

2. Initially Part B depends on the income , what if my income change in a few yrs ? would it be easy to adjust the Part B income base ? 

Always depends on your income level of prior 2 years on both Part B and Part D (2023 premium depends on 2021 income; 2024 on 2022 etc.), and you need to watch your income at 63 for starting Medicare at 65 and so on.

3. As someone mentioned , would it be hard to switch from MA to Medicap ? how about other way around ? 

Yes and no, really depending on where your residence and when. The other way around normally is easy. For the first year you have a free trial period for MA to freely switch back to Original Medicare. For later you need some special erollment envent like moving, your MA no longer avaialble etc. to freely swtich. Otherwise, you need to pass a medical underwriting (answering medical ? about your health), unless your residence in certain gurenteed issuing states (CT, MA, ME, NY). This is much more completed topic and here is a reference link from KFF:

https://www.kff.org/medicare/issue-brief/medigap-enrollment-and-consumer-protections-vary-across-states/