Howdy! It isn't a lot of cards. The longer you stay in these forums and look at the number of cards people have, you will feel like you don't have enough. LOL!That was how I felt originally.
Now, I can give some insight regarding AMEX and CapOne. For the most part, AMEX has been approving people with Experian FICO scores around 625 and up (Delta Gold, BCE and even the Platinum AMEX) . There are A LOT of people on these forums reporting that. I can personally say that I was approved for my AMEX Gold Delta Skymiles Card at a 638. I gasped. I never expected that. I have gotten offers since then for the SPG, EDC and the Hilton Honors. If your Experian score is around 645 and you do not have any negatives in your credit history you should be approved. Now AAOA (average age of account) does play a factor into that. I know that the BCE is approving with SL as low as $500.00. For now, I would say wait 6 more month and then pull the trigger. That way you will have the other account semi established and would have waited for a possible CLI. That would definitely solidify you getting approved. Of course nothing is 100%.
Side Note: With the CapOne QS1, they should do an auto CLI after your first 6 months of paying your bill on time. If you have $300.00 now it will probably go up to $500.00 or $750.00 depending on your score. Make sure that your income is up to date on the CapOne app so that when they do consider you for a CLI (which they look at all of the time) they will give you the correct limit. After you have had a CapOne card for 1 year you become eligable for a PC, depending on your credit. At that point, if you have a great history you could be considered for a QS or a Venture(One) with a lower score than normally required.
Good luck with your credit journey. Hopefully something I said helps you. You are almost there.