You can install Debian on the Kobo (in a chroot) that way you could do "native" builds directly on the Kobo itself (but compiling is a lot slower than on PC naturally).
Why do you want to build busybox? You can download a static arm binary from busybox site and it works better for me than Kobo binary. Kobo's busybox has really strange behavior in places, like `ls` showing no files even though they're there.
Some people just use the Kobo's browser to display stuff. It runs JavaScript, if all you want is a simple information display and don't mind slightly strange screen refreshes, that may be a simple solution. With my WebPortal mod you can also run shellscripts as CGI...
Standalone programs tend to be complicated because they have to do a lot. Touchscreen, eInk, and getting eInk to refresh properly... it's not always so simple. Then for sailing to be useful you need some kind of external input... GPS? Sensors? So you also need serial, or networking support. (again stuff you get "for free" with the Kobo browser, kind of)
For my own mods I pretty much avoided the issue altogether... at most I display an image or accept a simple touch input. I haven't done any full blown user interfaces yet (outside of the browser).
I think this thread was about using Kobo for sailing as well, might want to contact the OP for details
https://www.mobileread.com/forums/sh...d.php?t=256343