TJ and I have a travel hacking PM that's been going on for two and a half years... So imagine our excitement when someone brings this up in a public thread!
The first thing I'll say is the credit card game can be a slippery slope, you'll be tempted to get more and more cards, and outside of cashback cards each one works with a different currency. Sometimes you can find extraordinary value with each currency, but keeping track of each and managing them can be complicated and time consuming. Sometimes there are great deals with points, but finding them isn't always easy and sometimes they vanish in an instant. However, as engineers we enjoy the analytics of figuring out the best deals with each currency and the payoff in the end can be awesome.
For some people it's a fun hobby and for others it may just be a PITA to keep track of everything and in that case a good cashback card is a great option.
I managed to get two free first-class tickets to Hawaii for our honeymoon and paid for more than half our hotel nights there (13 nights total) with points. And this year we're going to Ireland for a week for free (free flights and hotel) with Delta miles.
The down side is I'm sitting on 600,000 Hilton points (worth around $3,000) and I'm not sure yet what I'm going to do with them. I'd love to use them on a villa in the Maldives, but that's a big commitment for using vacation time. And TJ finally convinced me to get a Chase Sapphire Reserve that I'll rack up a bunch of Ultimate Rewards points on that I'm also not quite sure what I'll use for yet... but hoping maybe to snag a couple business class tickets to Tahiti.
As for the Southwest question, if you really want to fly with them I'd second what TJ said about getting the two cards to earn the companion pass. If I recall correctly, that gets you priority boarding and some other perks too.