Make sure you've UTF-8 defined for charset and lang in your ~/.login_conf, otherwise almost every module will fail to install. Python 3 is very sensitive to that.
sudo pkg install python3 py36-virtualenv leveldb libxml2 libxslt pkgconf secp256k1 wget git
sudo wget https://raw.githubusercontent.com/bitcoin/bitcoin/master/src/secp256k1/include/secp256k1_recovery.h -O /usr/local/include/secp256k1_recovery.h
echo '#include "/usr/include/stdlib.h"' | sudo tee -a /usr/include/alloca.h > /dev/null
mkdir -p /tmp/venv_python
virtualenv-3.6 /tmp/venv_python/python3
source /tmp/venv_python/python3/bin/activate.csh
# these two modules fail to install natively
pip install ptyprocess eth-account
cd /tmp
git clone https://github.com/ethereum/web3.py.git
cd web3.py
pip install -e .\[dev\] --global-option=build_ext --global-option='-I/usr/local/include'
pkg install go
cd /tmp
git clone https://github.com/ethereum/go-ethereum
cd go-ethereum
make geth
cp build/bin/geth /usr/local/bin/
BROKEN (build crashes on FreeBSD 11.2)
py.test tests/core
py.test tests/ens
py.test tests/integration