i don't do the 3-4 month thing, yet i do apply for a new card roughly every month or two. if it's the same bank, then i will do both the same day, tho.

only one i have been denied is chase sapphire a couple days ago (CO, BA, and PC cards since Feb and two within past 3 months). called to move credit from one to the sapphire and was approved.

fwiw, i've never had to wait to apply for 3-4 cards on the same day. i usually just get them whenever i apply.

keeping them open, even if fee is waived, could backfire if you would be eligible for a new promotion. there are just certain cards i don't really want to keep open after a year, like CO and DL Gold and possibly HHonors Surpass.