EE for Software engineers
My answer is simply a reflection of my experience, so you may find it lacking in objectivity. Take it for what it's worth, but I would like to add my $0.02.

I haven't really found a good course or textbook on tinkering and learning how to approach hobby projects. To be honest, you don't really need any formal education to adopt the hacker/maker/tinkerer mindset. The way it works for me is I first choose a project I want to work on. I completely ignore all constraints (within reason). For example, the fact that I don't know a programming language, a specific technique, have certain parts, or have relevant prior experience are usually not my primary considerations. Choosing something interesting and useful is what works for me, because I am encouraged to learn and adapt to any situation in order to reach my objective. A huge part of the experience for me is learning something new. You already have a great advantage with your solid comp. sci. background.

From my admittedly limited experience so far, blogs, tutorials, and videos specific to what you are looking to do are best. For example, suppose you follow my path and ignore all reasonable constraints, and decide to build a device to water your yard. The first thing I would do is decompose what I need to build functionally. So I need something to understand temperature data and actuate the mechanical system, something mechanical to control the flow of water, something to detect temperatures, etc.

Then I would just go to Google, and type in any question I have. Something as simple as "how does a microcontroller work" will deliver superb results to you when you search for a way to control your project. You use these searches as stepping stones, and one thing leads to the next. Say you need to choose a temperature sensor, then you simply search for temperature sensors. You will find a lot of different kinds, but several which are very common and well documented - so go for those.

Again, my approach isn't as systematic and formal as what you may be expecting. Learning how to hack a device together takes a lot of passion, patience, and willingness to learn a lot of new things. Once you work on a few projects, you will realize that a huge percentage of your technical skills will become highly transferable.

So my last few tips would be:


Google is your friend, use it!
Read blogs (they are a superb resource, in fact, make your own to document and share your work).
Ask questions (places like here), but try to figure stuff out on your own first.


Search -> Read -> Ask (if necessary)

Again, it depends on what you're going for. If you're just doing stuff for fun, then I recommend my approach (works well for me). If you're doing some serious stuff, then ignore everything I said in this answer as I don't feel I am fit to give you credible advice.