Some improvements can be made to make stage3 simple to install. 
I suggest changing some init's:

• rc-update add NetworkManager default
• rc-update add haveged default
• rc-update add sshd default

I also recommend that some ebuilds be added to stage3 as they are essential:

• sudo
• vim
• networkmanager
• net-wireless/iw
• net-wireless/wireless-tools
• sys-kernel/raspberrypi-image
• sys-firmware/raspberrypi-wifi-ucode
• sys-boot/raspberrypi-firmware
• media-libs/raspberrypi-userland
• dev-embedded/rpi-eeprom

OBS: we need sudo as openssh server does not allow root to login by default. Look:

# grep -i permitroot /etc/ssh/sshd_config 
PermitRootLogin prohibit-password

or include regular user on wheel group. Regular user can only become root if he is in the wheel group:

# grep wheel /etc/pam.d/su
auth       required     pam_wheel.so use_uid

To emerge networkmanager, useflag from media-libs/gd needs update on /etc/portage/package.use:

>=media-libs/gd-2.3.0 png jpeg fontconfig truetype