I didn't mean Hirasa was a Byakugan technique, but that it was a technique of the Byakugan aliens. It is likely how they travel dimensions. I think you're right that the aliens extend their lives with the Chakra fruits, since Momoshiki does say that the fruits are what grants them immortality. On the other hand, the half-alien Toneri hasn't seem to have aged in 15 years, which might mean their long life spans could also be natural.We don't know the full pedigree of the Ootsutski clan yet. Hirasaka emanating as the property of the byakugan is still up in the air considering Ootsutski consume others in their arm which is also likely to be manifested with the chakra fruit. This could explain how Kinshiki prolong his lives span and thrive for the next centuries. Perhaps the higher ups of the Main Family institute a law to prohibit anyone to kill the Ootsutski member for that matter. Then again, the rinnegan on Urashiki appeared to be nowhere much like Kinshiki so the idea that the Joagan have the ability to enter portals which is the mutation form of the Byakugan is also possibility.
The "Big catch" might as well have to do with Boruto Joagan. Remember that the reason why Urashiki was set to motion in the first place was to stop Toneri due to influencing Boruto and hasten the development of the Joagan.
Yeah, he's most likely going after Bolt since this episode made it even more clear he wasn't interested in the Tailed Beasts.