That's a lot of questions!
Agreed, relying on WYSIWYG for a carreer is not the way forward. Open files developed with DW and try to understand the code: it never makes any sense and is pretty crappy.
So, being able to "tune" and correct these codes are essential, but this means learning how to code by hand, with a simple text editor. Those who CAN'T do that will remain forever (in my opinion, of course), poor amateurs.
So, what to learn?
It depends what you want to achieve. If it is only web development (I said "development", not "design"), you need just a few languages. Which ones is your choice and depends on the server(s) you will work on. There are Unix/Apache and Windows servers.
On Unix LAMP servers (Linux/unix, Apache, Mysql and Php), you need Php and mySQL.
On Windows, ASP, JSP, ASP.net and IIS db's. (I do not like window servers, hence can't say much about them, but they are Microsoft, and that's enough for me!)
Slicing: Aaahhh... It is not tought, because it is a complex "art". DW slices images for you in a way that makes me laugh: no meaning or functionality whatsoever. Slicing requires skills.
Let's take a simple example: go to www.web2coders.com. You can see three nice rounded boxes. These are "scalable", that is, they adapt to your screen width, whatever it is! This is done by slicing the box in 9 elements: the four corners are fixed in size, the center row expands/shrinks vertically to adapt to the contents, the middle column expands/shrinks horizontally to adapt to screen width. (Check the source code).
This slicing cannot be made "automatic" with any IDE: it requires "Human touch"...
So, if you need templates, make your own: I have never found any template on the web that works on all browsers and on all screen resolution!
As for Photoshop, sorry, but it is the best available (as long as you don't let it "slice" your images for you!). There are many places where you can "find a free copy", but I can't tell you here...