[ubuntu] Some issues with a new install

I am plaing to move back to Ubuntu (16.04) from OSX Mavericks on a Hackintosh (a HP 4540s). I have one disk ruing OSX and a separate disk for Ubuntu. My Users directory resides on a third disk, a usb disk, and has been configured to hfsplus non-journalled, and a test installation of Ubuntu loads the usb disk at startup though not as the /home directory. For the sake of those who may not know, Users in OSX is the equivalent of /home in Ubuntu.

I'm now ready to try a live installation of Ubuntu, and I'd appreciate any advice i can get.

• I want to mount the Users directory (it is a partition on the usb disk) as /home. I don't know how easy it would be to make the usb disk dedicated to Users. (Haven't thought about it, but it would require a deal of juggling.)
• My uid under OSX and presumably so registered under Users on the usb disk is 501. Under Ubuntu it will be 1000 by default. Same for gid.
• I have, of course, backups of Users, though in Time Machine format. Haven't thought about how difficult it would be to back up Users in another format, say, as ordinary files.
• I want to be able during the transfer phase to boot from either OSX or Ubuntu, since it will take some time to, for example, install and configure all program equivalents in Ubuntu. Just the thought of all my email accounts makes me blanch!

You MAY have seen a similar post somewhere else on the fora. I did post it once before, but did not make a note of the subject line, and now I can't find it. If you can point me to it, thanks! But I suspect that, for some reason, the post did not reach the fora.