WRT the resize of the root partition .. it is very simple to just resize it when you write it to the sd card with fdisk as soon as you are done on the machine where it is already mounted.

I guess it depends what you're using. I tried expanding one with a live CD Gparted once and it was a disaster. I had started using it though, thinking it had already been resized. I usually don't know the right block size to use with dd so I use Win32DiskImager to write images, and I have no partition table editor for Windows.

I suppose it could be unmounted safely enough but you should change the partition table before you start using it? Then again with splitfs that doesn't matter.