Your idea to flush out the delivery valves by cranking with the hard lines disconnected will probably get rid of any of the debris you described. It is common to have small pieces of the old o-rings and minute metal shavings in there. I had them and cleaned them out as best I could and didn't flush at all and the car hasn't suffered one bit, but that's not to say it wouldn't have been a good precaution to flush them like you thought...so do it and then reconnect the hard lines, crack them open at the injectors to fill them and close them up and start the car...all should be fine. You might need to jump it if you kill the battery with all the cranking, I know I did, but I replaced all my fuel lines too and it took a lot of priming to get the system full of fuel again.

Good Luck!

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Marty D.

2013 C300 4Matic
1984 BMW 733i
2013 Lincoln MKz