Looks interesting. From an aesthetic point of view, you might consider shrinking the header down a bit. It takes up a lot of the screen area and doesn't do anything practical (it does look nice, though).
Yes, filling up space with a pretty graphic just means people won't see as much of the interesting stuff when they land. By all means brand each page, but don't push the main content too far down for the sake of it.
Also, I think the search box should be up the top of the page where most users will expect to find it, rather than in the footer.
Yes. Searching for the Search bar is a bit paradoxical.
Navigation:
The menu item: "Before Arduino: Extremely Brief Electronics Introduction" goes to the section titled: "Furthering Our Understandings". This could cause some confusion when people navigate - "I clicked there and ended up here??". I would suggest the title in the menu option is the top title of the destination page.
Proof reading:
In clicking on the "Before Arduino: Extremely Brief Electronics Introduction" section, there is a sentence in the section about GND:
"See the diagram on the right for a simplified view of the schematic on the right." One of those "right"s should be a "left".
Further on the proof reading task is the clarity of expression - that is, how well you have phrased the ideas you want to convey. I would suggest someone who is good with words, but
not technical, has a read and let you know what bits were confusing.
Structure: At the moment, you have one set of options. While the content has few entries, this isn't a problem, but if you end up with 200 or so little tutorials, this might become unworkable. I suggest you sit down and map out what your content might look like in a couple of years' time and think how it might be organised. This does NOT mean you set up 3 levels of menu with lots of empty spots (until you get the content to fill them) - just be aware where you hope to be and plan for migration to a more involved menu structure. The balance is to try to keep the menu hopping to a minimum, but not overloading each page with too many entries.
Titles/Naming: As an example, at the moment, you have a section titled "Before Arduino: Extremely Brief Electronics Introduction". While you stick to Arduino, this isn't a problem, but you have mentioned PIC. If someone comes to your site looking to follow only PIC info, they probably won't see the "Before Arduino" sections as relevant.
Just some thoughts. I don't pretend to be an expert - so make up your own mind if any are useful.