Yes.

What if I can't find a job before visa number becomes current?
-As long as USCIS does not send you RFE for your employment status, your I-485 is safe, but if they ask RFE, you may be trouble. So, find a job as soon as possible.

And If I find a job, do I need to keep H1b or easily use EAD?
-If you can find a job in short period of time, your H1 transfer may still be approve and thus, you can keep H1 status. Otherwise, just use EAD to work.