1) You need to win the H-1B lottery and then can do a CoS (Change of Status) to from L-1A to H-1B. If you don't have H-1B approved petition in hand, you can't do a CoS and have to wait for next year's lottery.
2) You'll retain your I140 priority date but your H-1B employer will need to file for I140 again. And this time you can't apply for EB1C since won't meet EB1C criteria with new employer.