re: Opening new personal credit card for rewards purposes. Which one’s right for me?

Honestly, when people ask me in real life what to do when they find out what I do with CCs, I tell them the truth.

If you aren't willing to do hours of research on the various programs, having logins to possibly 10-15 airlines, comfortable figuring out what time of day to call a Japanese airline to get an English speaking representative, spending hours of time researching availability and seeing what time seats release for booking (usually in the wee hours of the night), so that you can have a chance at booking two business class seats, on days you actually prefer, then I tell them get the best cash back card each bank offers and rotate among them.

Otherwise you're going to kill so much value as to make it not work out. The amount of effort I put in if
honestly valued probably eats a lot of the gain, but I approach it as a hobby.

ETA: As for that $300 credit. Credit where credit is due by Chase just making that a simple reimbursement from making purchases. Now, if they had the choice to do it now they'd probably force you to their travel portal (like the $50 credit) but they didn't have a strong operation there when they launched that card. Of course Amex has taken the coupon book to incredible heights.