The tutorial on the link above will give you a mobile version of your email in the Gmail app, as it doesn't use media-queries. Give it a whirl!
Totally doable with your content I think. It'll take a little time to get your head around just how things work in hybrid. Working through that tutorial helped me. It just gave me the understanding of what the approach did in terms of email coding. Once you've got the basic understanding down, it's easy to apply it to your templates.
Your template is very strongly structured with rows and columns, which is the crux of the hybrid email theory. The kind of things you will have to keep in mind will be things like being unable to specifically align certain elements/text for the Gmail mobile app. For other mobile devices you can use media queries, but with Gmail you're relegated to just sticking to what you've got in your inlined CSS. Little things like that. But if you can make those concessions, you'll be fine.
Signed, Sealed, Delivered - Stevie Wonder
Weapon of Choice - Fat Boy Slim (well, email's my weapon of choice ;))
Bounce - System of a Down
Galaxy Bounce - The Chemical Brothers
I can't find any update notes online or anything of the sort - why would Google do a gmail update and not make anyone aware of what it is exactly that they've done?
Pretty standard way they've been updating Gmail ...!
Unsure about classes, but what I have learnt with going down the hybrid/mobile first approach is that you do have keep it in mind at design level. While hybrid emails should be the standard, they do have some limitations you just need to be aware of, mostly for the likes of Gmail/Gmail app.
I used this tutorial by Nicole Merlin as my intro to hybrid email coding - http://webdesign.tutsplus.com/tutorials/creating-a-future-proof-responsive-email-without-media-queries--cms-23919
It's not a class, but it's a great walk through if you follow along with the example.
Another vote for Litmus Builder and the ability to share HTML previews built in.
One option could be loading up the HTML into your ESP and sending out test emails to your colleagues. But if there are amends to your HTML after sending to colleagues, it'll add time to your email workflow.
Another option would be to use https://putsmail.com/ to send them the HTML to their inbox.
For the HTML you just need to add this to your meta tags:
<meta http-equiv="Content-Type" content="text/html charset=UTF-8" />
However, as this is happening in the subject line, adding this won't help, if UTF-8 isn't set in the email header, which is set by the server sending the email. Contacting your ESP might shed some more light on this.
You could try using
instead of the £ in the subject line too.