I would have used a 1080p 60 fps timeline since 30 fps footage will playback perfectly while keeping the smooth motion in the 60 fps video. When done, render out to H.264 Blu-ray to 1080i using the HD 1080i 29.97 Preset.
Adding 720x480 footage to a 1080p timeline would require you to upscale the 720x480 and it will look not-so-good. Depending on the project it may be worth editing the 720x480 on a separate timeline and render it out as 720x480 and thus forcing the Blu-ray writer to upscale the footage. Software is not so good at upscaling while hardware, iow the Bly-ray player, is much better.