Hi Carl,
XPages will run in the Notes client but only if you're clients are 8.5.1+. For earlier Notes clients, your users would need to access XPages applications using a web browser.
For web development, I would highly recommend that you go for Domino 8.5.1 as it has a huge number of bug fixes compared to 8.5.0.
In terms of training options, there is a ton of resources for free out there to get going with:
are all good starting points.
Hope this helps.
Matt