Can I report to new company-O and apply vacation in current company(C) until I get H1B transfer approval?

Detail: I am in H1B with company Current(C). Company C has initiated Extension *** Ammendment petition(New) in normal processing on March 1st and I got the acknowledgement receipt. At the same time, the validity of previous extension petition expired on March 18 and I94 Expires on March 28. Meanwhile, I have got... show more Detail:
I am in H1B with company Current(C). Company C has initiated Extension *** Ammendment petition(New) in normal processing on March 1st and I got the acknowledgement receipt. At the same time, the validity of previous extension petition expired on March 18 and I94 Expires on March 28.

Meanwhile, I have got new offer from company Opportunity(O) for a different client.

Question:
1. The new company got an client letter mentioning 4 months of duration and subject to extension. According to trend, Does this duration affect chance of approval?
2. Is it advisable to initiate H1B transfer to new company-O using the acknowledgment receipt?
3. Is it legal to initiate H1B transfer to new company-O using the previous petition(expired on March 18 and I94 Expires on March 28) before March 28th?

4. Once H1B transfer is initiated in premimum, can I report to new company-O and apply vacation in current company(C) until I get H1B transfer approval?
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