Change job with work permit B

Hello,
I am a non EU citizen and have been working in Belgium for 4 years, I have got 5 work permit B, I need to change my job, and the new employer will offer a permanent contract to me and help me to renew my work permit B.
My question are,
Is there any risk that I renew my work permit B with such approach,what I mean is that I may fail to get the renewed work permit B, as I my new job position is totally different from current one.
And how to ensure there will be not any interruptions between these 2 work permits? Do I need to negotiate with both of the current employer and new employer? Can anybody share some experience?
Is it better to apply work permit A or B this time, as my plan is to apply 5years residence next year. Not sure if I apply work permit A will impact or not.
Thank you.