Normally I advise against static IP addresses, but an isolated network is one of the few valid use cases.
You can connect to the Pi over a direct Ethernet link to the Pi (not via a switch or router) using the Link-local address, although discovering this can be problematic.
You can easily connect from Linux and OS X with
ssh email@example.com (the default hostname is raspberrypi) This should work with popular GUI ssh programs. This is sometimes problematic with some versions of Windows and networks which use .local in a non-standard way. (See https://en.wikipedia.org/wiki/.local)
The other alternative is to assign an IP by including something like
cmdline.txt. See https://elinux.org/RPi_cmdline.txt
I have not used the last in a modern Raspbian using
dhcpcd, but it should still work, and should be replaced by a normal configuration.
ext4 partitions from
macOS is difficult, since the introduction of SIP. There may be 3rd party (paid) solutions which work.