why not just use a regular encryption software like anon above suggested? encrypt your drive and on top of that 128-bit encrypt your super sekrit data. something that'll take 300 years to decrypt.
Also BSD is kinda hard even if you know linux already, because many tools are quite different and many of them are configured in such a way that you need to use switches for things gnu tools detect automatically.
They're pretty much like netinstall yes. I tried FreeBSD and couldn't configure dhcp for the life of me. I ended up coming back to gentoo
Encrypting your harddrive isn't hard but it's not given as an option in the installer. Follow the OpenBSD section of http://www.bsdnow.tv/tutorials/fde
Do miniroot + sets.