I'd be happiest if they kept to the style of music normally used in the series, with the exception of the opening song.
For example, I'm perfectly content with an upbeat melody opening each episode, similar to how "Peaceful Valley" did in LBT 2. The difference being, LBT 2 also consisted of a lengthy instrumental opening prior to the first song. I would not expect such an opening in a TV episode, as that sort of "epic instrumental" seems more in-place in a feature-length film as opposed to a weekly cartoon.
The music during the episodes could be very similar to the music used in the films. The atmosphere is presented well in most cases, and the style is well suited, as even associated with, the LBT series. I see no problem with including the "If We Hold On Together" themes in the music during the shows, as well as other James Horner and Michael Tavera themes. If the team hires a new composer, I hope he or she continues with the basic principle of LBT-style music. I'd hate to see the TV series drift too far from the films, and continuity of the music is one way to run the TV series in parallel with the films.
As for the end credits music, I think it could very from episode to episode if the developers wanted, however the most logical use of music for the end credits would be the classic choral/orchestral version of "If We Hold On Together" played at the end of LBT 4 and other LBT films. If Universal wants to keep a consistant End Credits piece of music, this would be my first choice. Of course there is also the option of changing the End Credits music for some episodes. This music could depend on the atmosphere of the episode it is concluding (for example, the "epilogue" music in the final scene of LBT 5, going into the end credits, was very well-suited in my opinion).