JetPack 3.1 is the most recent production release…this will install L4T R28.1 during a flash. JetPack 3.2 pre-release is out…I think this installs L4T R28.2 pre-release. Both run Ubuntu 16.04 (L4T R28.1 and R28.2 are Ubuntu 16.04 with NVIDIA hardware accelerated drivers on top).
If you don’t need to test something you may want to start with JetPack3.1…but yes, flashing should be one of the first steps since the original L4T R27.0.1 which a TX2 ships with has had a lot of fixes since then.
JetPack was designed to run on Ubuntu 14.04 x86_64, but mostly runs on on 16.04 (I think a demo package might not work in 16.04). It is highly unlikely it will run correctly in 17.04…at least not without effort, and I’m not sure what effort would be required.
If you just want to flash you can use command line via the combination of the driver package and sample rootfs…JetPack is a front end to this plus package installs. Any Linux x86_64 desktop PC works for command line flash.
Note that if you flash the Jetson and later on wish to use JetPack to install packages there is no problem. JetPack can have steps to flash unchecked, and software added or removed at any time…JetPack just has a default to flash via a checkbox. Using command line flash and then JetPack works without issue.