Depending on the card, I'll keep it. I also usually call in and try and get them to waive the annual fee, which works most of the time on the 3rd or 4th call.
I opened 25 cards in the past two years and I'll be keeping most of them. I'm expected to pay about $750 in fees a year to reap some nice rewards.
For the Chase Southwest Cards, you would first have to spend $2k on each card ($4k total) to get the 100,000 points (50,000 each). Then if you want to, you would spend $6k additional on the cards to get 6k miles on each card (totalling 12,000 miles).
Once you hit 110,000 miles within the calendar, you will earn the companion pass for that year and the following year. Remember that the points will post after your chase statement date, so you don't mess up and don't get the 110,000 miles within the calendar year.
Also, for Chase's 5/24 rule, they aren't really that strict with it, you can bypass it by going in-branch and checking if you are pre-approved for certain cards.