personally unless you have some huge purchases coming up, most people tend to go on a app spree. Unless your in the market for a new car or a house anytime soon I would apply for it til I started getting declined, applying for harder to get cards first. BCP then Chase Sapphire , US Cash+ , Citi Dividend seems like the way to go in order from what I understand about them. Amex is stricter
Quicker you get things, the quicker they'll all age together.
example is if you had no cards ever, and got 2 now, in 6months your AAOA will 6months, get 2 more cards then and you'll have AAOA of 3months. If you got 4 cards now, then your AAOA is 6months.
but since you already have Amex already personally I would apply for it in January. Because of how backdating works. Backdating takes the month of your new application (Jan if you apply then) and takes the member start year. So if you get a BCP approved in January your BCP card (assuming you started in 2011) will show an age of 24 months when it first reports.
Also remember that if you get approved other companies will not know about the other if you do it on the same day since inquiries take atleast a day to post to your credit report, so it won't be a deciding factor the number of inquiries if you do it all at once. Also remember that if you over app when the companies run a soft check you could get all your accounts closed due to credit pyramiding risks.
Pretty much what distantarray states.
I'm one of the heavier proponents of app sprees; the math just doesn't work out over the mid/long term to do them in batches assuming you can get approved for them earlier, and everything is time dependent in the FICO model anyway.
End of the day, if there's a card that you want and you're able to obtain it (vis a vis if you can get a CSP you can get a BCP 98% of the time) then it's in one's best interest FICO-wise to just establish the tradeline as soon as humanly possible. Backdating from Amex does factor into changing that somewhat, doesn't make sense to apply in October when you can wait for January as an example, but other than that or if you're planning on a mortgage or possibly car in the next year, app sprees win out FICO wise: short-term increased damage, longer term overwhelmingly positive when you napkin math the factors.
The constant application method every six months really doesn't hold up either for FICO or for the current economic environment; however, much of the current common wisdom on this forum was garnered in the belt-tightening days by the banks and everyone proceeded more cautiously as a result. I don't see the purpose of stretching out the pain of inquiries and new tradelines any longer than required.
@ccnewcc wrote:How many is too many?
Apping for 6 plus the 5 you already have.
I know many ppl on here that have many many cards. I tend to think that only 2-3 are enough.
Of course SD and cancelling ones you don't use/need is an option, but again 2-3 too me is plenty.
I don't think it's nessasary to have every card, cash back ones are ok, but on the ones based off points becareful, cause if you don't use it enough you'll never be able to spend it =p
Few things like we all need Gas so PenFed 5% is nice BCP 6% back on groceries US Bank Cash+ for 5% on restaurants and 5% on billpay covers almost everything for me, I don't spend too much out of those circles to really matter imo. Although Discover more has a great category for Holiday shopping 5% back online and department stores.
@ccnewcc wrote:How many is too many?
I would probably say don't go past 6 at one time, but people have been known to get 26 inquiries -_-; when going on a app spree avoid companies like capital one who pulls all three bureaus at once and save those for the end if you really want one like the Venture card which is pretty good.
I do in in bunches. For instance last June I did a spree for auto loans, probably 10 or so all within a two week peroid. Those witll all age off at the same time this June. I also had another this past September/October, those will all age off at the same time too. Hopefully my CS will improve after all the June 11 age off.
Grin, how responsible can you be with them if you don't know exactly how many you even have? 
All kidding aside, more is not necessarily better; I find the thought of 20 cards a little horrifying for a few reasons when I play "what would an underwriter think?"
I'm not sure where the more positive accounts you have is better for FICO came about nor am I confident it's correct; however, everything suffers diminishing returns in the model anyway and for scoring purposes three is just fine, twenty isn't needed, and utilization can be handled via payment timing without substantial effort.
I don't see an upside of being able to play a reasonable facsimile of 52-pickup with one's credit cards .