The Firefox web browser will be our go-to browser for these workshops — you should install it even if you usually use another browser, because it offers specific features that we'll eventually depend on. Available for basically every operating system you might ever consider using.
Demoroniser is a Perl script for more technically savvy users and can also help to clean up some of the awful cruft that Word shoves into the HTML that it exports. French speakers will appreciate the pun in the script's name.
Useful, free graphics software
If you already have graphics software you like, why, by all means, you should use it. If you're looking for good free software, though, I have some suggestions.
Inkscape is a free, powerful vector graphics creation program for Windows, Mac OS X, and Linux.
Dia is a useful diagram-creation program for Windows, Mac OS X, and Linux.
Scribus is a powerful (and free) page-layout program that can also be used to create vector graphics. Available for Windows, Mac OS X, and Linux.
There are a lot of upsides to hosting many types of content externally: you can leverage other peoples' work in preparing a functional user interface, you don't have to (or, at least, may not have to) pay for storing your content or the bandwidth involved in transferring it, and the external host may have tied social network–sharing functions to your content at no additional work on your part. However, there are also downsides: you're relying on someone else to hold on to and serve your content, so you need to ensure that they're reliable and likely to continue providing the service, and you need to abide by someone else's terms of service, which may or may not have hidden gotchas or prohibit certain types of content or otherwise restrict you. (A case in point: in February 2016, I discovered that ImageShack had changed their terms of service without even bothering to notify me, and that images I'd used them to host had silently disappeared from my website. Hey ImageShack: silently dumping all of my content with no warning is a poor way to get me to convert to a paid account, or to get me to continue recommending you.)
That being said, I tend to find it worthwhile to save money and gain other benefits by hosting large files elsewhere, provided that I keep my own local copy. Here are some service providers who will store and serve content for you, presented with the caveat that you should read the fine print and make decisions about who is a trustworthy provider on your own.