I haven't tried it, but maybe it is possible to install dev.mode by manually downloading and installing the deb-s?

I have no idea in which order these should be installed, or should they all be installed or maybe just few selected ones will suffice.

Maybe, if you don't need root access, you could install apps by hand using file manager. Install your preferred file manager by transfering it to the n9 via bluetooth, for example, and then starting an install from the transfer window. Could be, that devices date should be set back to 2015 or earlier for install to succeed.