Welcome SimonsMiles
I see in your profile you are based in London, England. So it could be a smart move (i.e. a not too silly one) to consider European FFPs, just to maximize the benefits. In my opinion AA has a great FFP, but if you are not in the US you can not really use a few benefits like the upgrades.
My 2c could be to have a card each for OW, *S and ST. Which ones ?
OW
I could start BA but the TP trick is quite annoying and the BA/AA transatlatic problem is quite irritating. I could say, use the BA to reach a nice number where you can have a nice flight (e.g. 50K is UK to Hawaii R/T in Economy) and then switch to a common program... i.e. a program where you can place ALL the OW flights, for example the Finnair one, where yes, you can place all AA and all BA and all other OW flights. By the way are you aware of TESCO to BA point conversion ?
*A
No way, stay with the BMI Diamond Club (BD). Read a bit more about it in the proper forum and it's really a good program, always in my opinion... o/w at 50%, biz only 50% more, first at 100% more, cash and mile (^ ^ ). Try LHR-HKG with NZ in business and let me know. And go on with the DC credit card.
ST
Be calm, be seated, fasten your seatbelt... go for Alitalia Millemiglia. The reason is the minimum number of miles, 1200 ! Quite easy and very soon they could be wiped out or merged one to one in the M&M of Lufthansa or in the ST FB of AF/KL.
Hotels
Stay with Hilton Honors and go for Diamond. Diamond brute force... you always get a room, even for award... only exception only if the property just burned to ground. And with the double dip you can get 1000 BD miles per night (max 3000). It's a booster.
With 30K PC points you can have a wonderful 1 night stay at an IC... try Le Grand in Paris, perfect for a weekend. And be aware of the many promotion PC runs, like a lot of 10K bonuses and double points/miles. And to be sure just do the on-line survey on its main web page... 250 bonus miles. Marriott Reward is great also but you need to be at least Gold to start having real benefits & savings, their travel package award can be soo good, 235K MR points for e.g. 120K AA miles and 7 nights at any category 1-5 property. By the way are you aware of Marriott Reward to TESCO to BA point conversion ?
Be aware of any rule of deletion (usually after 3 years of idle time)
Enjoy