I often see third-party FreeBSD desktop guides that include this:

# pkg install xorg xfce4 slim
% echo "exec xfce4-session >> ~/.xinitrc"

Xfce remains my pragmatic favourite after all these years. But WindowMaker is also wonderful and nostalgic, and tiled window managers are for squares:

# pkg install windowmaker

The guides then advise you to configure these /etc/rc.conf services:

moused_enable="YES"
dbus_enable="YES"
hald_enable="YES"
slim_enable="YES"

This is all fine, but moused isn’t necessary. From the manpage:

The moused utility and the console driver work together to support mouse operation in the text console and user programs.

Your mouse is almost certainly using the xf86-input-mouse driver automatically, unless you don’t install the Xorg metapackage.