Jpeg does not support transparency. GIF does, by identifying pixels that are set to be transparent, but it does not support translucency, which means that there is not a smooth transition from opaque to transparent pixels.
PNG24 is what you need for transparency.
As for uploading content -It sounds like you plan on hosting the site on your own server, which means that you would need to have a number of things in place.
Unless your content is highly secret stuff - such as requiring a password to view the site, there is no concern about having your site on a hosting service - just use a reputable one such as GoDaddy. Using GoDaddy as an example, they are hosting literally millions of sites around the world. If there were security issues, it would get around very fast. I’ve been using them personally and for corporate and business sites for some 12 years and have never had an issue. And they have tools to make things as secure as you like.
If you are concerned about people grabbing your images and content, the only way to prevent that is to create some sort of transparent overlay. Even so, people could easily so a screen zoom and grab a screen shot.
Regarding the book, it covers everything that is in the Windows version. It is not a major in-depth reference book, but a bunch of tutorials. It will not go out of date any time soon. BTW, the Mac version of Designer (also Intel based) has been out for several years and is very solid, so they have an excellent stepping off point for Windows.
You will be needing some sort of bitmap app if you’re not using Photoshop. If I might make a suggestion - you can buy used copies of pre-CC / permanent license versions on eBay and cheaply. Something like CS 4 or earlier will fit the bill.
Another option (feel free to dismiss it) is to pick up a used Mac on eBay. It will open the gates to tons of software not available on the PC (including Affinity Photo), and the Mac can also run Windows (either / or, or both OSes simultaneously, plus they can share peripherals. A real-world benefit of having both platforms is that you can test your websites properly, using browsers such as Safari, as well as older version of other browsers. Windows machines tend to display colors slightly darker than on the Mac (Windows users tent to crank up the brightness) and sometimes, especially with low-contrast fonts, a site may look great on a constrasy Windows machine, but be harder to make out on a Mac. Roughly one computer in ten these days is a Mac and studies consistently show that Mac users tend to spend more time on the Internet than Windows users, so being able to test a site on a platform that can represent around 15% of users is worth considering.
Of course, this is only a suggestion. For myself, I run Windows XP, W7 and W10 on my Mac (simultaneously) and have a range of browsers installed on each copuy of Windows (including different versions of the same browser). This has been extremely valuable, as it shows me where things can go wonky so I can make my sites look good on all OS versions. (Even when a person doesn’t care about the Mac, being able to run multiple versions of Windows for testing purposes and have them all running at once is a huge boon.) Feel free to tell me to jump in a lake. No offense taken.