Glad to hear the flash drive now boots at least
As far as your new installation goes I take it you're trying to install it in EFI mode.
Also you need to make sure that your Mac is using GPT solely - as in no hybrid mbr (which is what a previous BootCamp partition will have created - if you've had one) as going past 4 partitions with a hybrid mbr can be dodgy.
Did you install grub? I elected to select "try Ubuntu" first then ran "ubiquity -b" in the terminal so that grub would not be installed at all (rather than just setting the Ubuntu installer loose).
Then, once installed I booted into OSX and installed rEFInd and placed rEFInd's ext4fs driver in a new folder called drivers which I placed in EFI/Boot iirc - I can check that later.
Did you press the Alt key whilst re-booting the Mac?