How do you strike a balance between supporting and developing emerging talent from within the organization, and identifying external talent that can bring in fresh perspectives?

A very important question. You need to start with what is your business strategy and find the balance to develop from within (build) but also to buy certain skills by hiring external talent. If your company has an ambitious ESG agenda, you won't be able to accelerate if you only develop from within, you will need to get expertise skills in. You can then use those external hires to help develop from within. You need to make sure that your employees see the type of new skills that are being brought in and that they don't feel that old the cool jobs go to new people so you have to be ready to elaborate why you are hiring externally. Also you need to make sure you keep your workforce diverse from a knowledge and skill perspective.  

This is a critical point for most businesses.
Developing a cohesive approach to talent starting with performance management to identify development needs can feed into internal talent, succession and also any external talent requirements.
This is my most enjoyable piece of the HR puzzle and the best way to showcase how people teams can make a real ROI for the company!!!

I think you have to have a measuring stick for the internal talent and what is on the bench for succession planning versus the need to go external. Being able to discuss and have objective talent assessments, not anecdotal insight, on your leadership levels at a minimum is important. Have to know based on peer and direct leadership who is ready, not ready or may be in X time frame to build out the bench for promotion and even assessment of competency gaps to grow internal. We have started putting rigor around talent conversations with framework of targeted questions of the individual employee about where and how they see themselves and also the same from peers, direct leaders and/or other leaders outside of area that work with them. This gets you to know the gap on your bench for succession planning and what roles if they come vacant you need to immediately go to outside recruitment versus what may be waiting on the bench.