Output is HDMI *or* Composite, never both. Composite refresh-rates are defined in common kernel code (not Amlogic driver code) and implement the broadcast specs for NTSC or PAL, neither of which use 59.94 output.
Kodi does not support dynamic reconfiguration of itself each time you switch display device (although it is mildly tolerant of changes within the same display techology, e.g. one HDMI device to another HDMI device). So install the device to the screen that you intend to use and the leave it in a working state. If you keep switching, expect it to keep breaking.
If you connect Ethernet the default route will switch to Ethernet. It's possible to change ConnMan behaviours by copying the config file in /etc/connman/main.conf to /storate/.config/connman_main.conf and changing PreferredTechnologies = ethernet,wifi to PreferredTechnologies = wifi,ethernet then connecting Ethernet won't steal the default route.
I've no idea about analogue audio output. The p201 device-tree file does not implement support for analogue audio, but that's not unusual as on most GXBB (S905) designs the DAC is hardwired (always on) so there's nothing to enable or control from software other than the global (master) volume level. If your box is different and has a controllable DAC chip it will require the driver to be enabled in the kernel config and the DAC chip to be described in device-tree; and then you'll need to script post-boot changes to the default mixer settings (which are configured on boot for HDMI output) to switch i2s output to the DAC chip.
NB: If you want something cheap that better supports Composite output, my suggestion would be to use an RPi board. Composite on Amlogic hardware isn't something that's ever been tested by me (as I have nothing that accepts Composite input) so our images are oriented towards HDMI usage and you're probably going to fight the OS at every turn.
LE does not implement boot menu's so no idea what you're talking about there.