Hi Xiaohu,
you're asking many questions. That's fine, keep going... But if you feel the need for some basic literature, let me know. This may answer many questions. Here's one page where you could order the "Bouwplan voor Kistorgel" book: https://www.johnboersma.nl/bouwboek3-english.html but I don't know the regulations for sending to China. I would certainly build details differently that described in that book, but I like it as a source of inspiration. In general, get as much inspiration as possible and look at many different instruments as possible, live or via internet or books. There will be many "aha" effects where you will think: That's a neat solution, I'll take that one!
Back to your question: It doesn't matter how the air arrives at the pallet box as long as it is stabilized (pressure regulated) and the opening to the box is big enough. You can pressure regulate externally by a bellows/ventil combination or you can build it into the pallet box. Having an external bellows can make maintenance of it easier but it makes the instrument bigger. One solution for that is building it into organ bench. There are even builders that build whole pedal registers into the bench like this one: https://www.youtube.com/watch?v=vfAWUfV-tsY.
Regards, Jens