ubuntu and osx full disk encryption easily possible? what about dual graphics?

hello,

i got a macbook pro 9,1 (mid 2012) and plan on finally switching from osx as main system and windows for games, to ubuntu as main one and osx just for firmware updates.

how would i do that, while still being able to use the full disk encryption from the ubuntu installer (so easy). because last time i tried, w/ my osx volume fully encrypted, w/ recovery, ubuntu would only let me use fde, if i had erased the whole disk again and started over.

osx full disk encryption isn't really needed, if i plan on just keeping it around for updates to the hardware.
or would you just kill osx altogether? and boot it from an external hd, if there's a hardware update available, or i wanna edit/disable my firmware password.

another question, can i easily switch between the graphic chips? and do they auto switch like under osx? i like the power from the dedicated on at home, while having a charger and the low power usage of the slow one.

i'm so excited to finally have everything i need on ubuntu, a beautiful, minimalistic interface, a good backup solution, spotify, steam a lightroom alternative and proper macbook support (at least based on my last test) and soon the last one, the plex client.