I hold a B1 visa currently outside the US and I have an employer who is processing my H1B visa do I need to apply for another?

You should probably wait and have the employer file a d get an approved H-1b with which you can then return to the embassy and obtain a H1b nonimmigrant visa. Coming to the US with a B-2 visa when your intend to work may become a problem for you alter

Once your H-1B petition is approved, if you are outside the US you will need to apply for a H-1B visa on the basis of that approved petition so that you can enter the US with that visa and commence employment with that employer.

Yes, assuming you are currently outside the US. Once your employer and you receive the I-797 Approval Notice for your pending H-1B, you will need to arrange to consular process to get your H-1B visa actually issued and stamped into your current passport (which should have a remaining validity of at least six months).