Thanks to XRG81 for providing detailed low poly texture painting and UV unwrap tutorials in Blender.
Some of the things I have learned:
Simply drag reference image into blender Front viewport.
Hold [CTRL] while using inset [I] to extrude.
Press comma [,] for orientation (axis) wheel menu.
Press period [.] for pivot wheel menu (center of rotation / scaling).
Press [SHIFT][S] to set the cursor to world origin.
For symmetrical objects mirrored along a world axis, when in edit mode you can scale vertices / edges around the cursor in the origin to stop them from entering the mirrored side of the object.
When in vertex mode with vertex snap enabled, you can press [A] to mark surrounding vertices. The selected item will now move averaged between these vertices. This is very useful for centering objects.
To connect separate parts in your single object, make sure they overlap. Then use [Faces > Intersect (Knife)] to create edges where the faces intersect. Make sure to select [Source: Self Intersect] in the popup tool panel.
Select a single vertex. Press [SHIFT][CTRL][B] and move the mouse to perform a bevel on vertex level.
Things I have learned: