2 h1 petiton, first approved, SSN and other concern

[h1seek]

i have filed two h1 petitions. First one is approved. waiting for seconds approval. i had following concerns :

1) if we have filed two h1 petitions and one h1 petition is approved and waiting for second h1 approval, does the SSN office explicitly need the employer that m gonna start working with ? or is the SSN generation independent of the petition approved ? can i specify employer 1 for generating SSN and later on start working with employer 2 if his terms suit and inform SSN office about employer 2 petition approval and starting employment with employer 2 rather than employer 1 ??

or i need to wait for both petitions approval and then decide which one to use to apply SSN ?

2) my understanding is that on receiving H1, one should start working the next day of the approval, if the approval is post October 1st. But employer mentioned that i would need SSN to start working. But as per my knowledge, on H1 approval post October 1st, a candidate should start working and his/her salary slip should be generated , else he/she can get out of status which can create complications further, if not at the moment. Kindly advice on this issue.