Since your QS1 doesn't have AF, I would combine the Platinum with it. The Plat would be cxld and your new QS1 CL would be $6.75k.
Normally both cards need to be at least 6 mos old and the Plat would need a zero balance. The bigger QS1 will be ineligible for CLI for 6 mos.
As far as PC'g that card to Venture or QS Visa possibly, but I wouldn't recommend it. The APR wouldn't improve and you would forgo any bonuses for Venture and QS Visa.
I'd chk prequal and app for new QS Visa or Venture. Once that card is 6 mos old combine the QS1 with it. Good luck!