We will not write how to install FreeBSD as it's simple enough that anyone should be able to do it themselves without much trouble, starting over won't be much of a problem as long as you've documented your steps properly.
With that said here's a guide in swedish on how to do an installation with gnome.
Note that we will not install gnome on our server so on step 4 in that guide pick the "minimalistic"option and you will not need a boot manager either since your OSdrive should be the first one.
The handbook is your friend!
http://www.freebsd.org/doc/en_US.ISO8859-1/books/handbook/