Great questions! Pursuing the IP strategy is certainly not for all game developers. But in regards to your questions:

1. Costs — The costs of going after large IP comes down to time, revenue splits and upfront costs. Obviously exact costs vary from situation to situation. I know super general/generic answer. If you are looking for something more specific you can DM me on Twitter, and I can try to help.
2. Potential Saturation — Usually licensors cut up their license based off game genre and geography. Licensing uniquely off of these attributes. This is where game developers can look at their competitive advantage and review if their genre or gameplay makes sense with that IP. Kabam would never do an endless runner and therefore would not go after IP that made a lot of sense with that genre.
3. Emerging IPs are best considered when you can lock up content and channel. What I mean by this is exemplified by a company in China called iQiYi (爱奇艺）and a show called Hua Qian Gu （花千骨). iQiYi had exclusive ability to distribute this show, when they released the show they also partnered with a game developer to make the game, funneling all the players into that game. That game made over $100 MM USD for the year.

For game developers trying to break into IP, I would say start with your strengths — what genre or gameplay is your team really really good in? Go after IP that would be a great fit for that.

And if you are making original IP — what celebrity or influencer is a great fit to help you market it?

Hope that helps!