Converting comments to answer, as requested:
The Dandelin spheres answer question (1): a focus of a conic section is the point of tangency of its plane with one of those spheres. Clearly, the point on tangency lies on the cone axis if and only if the plane is perpendicular to that axis; therefore, the axis contains a focus in, and only in, the case of a circle. The axis point has some relation to the conic section, but not one as interesting or useful as a focus. (As for "Does the diameter of the base of the cone pass through the focus of the hyperbola?": note that the cone has no base. The thing extends, and expands, infinitely-far.)
This notion of points seeming to move "out to infinity and come back on the other side" is not uncommon in analytical geometry. (It's kinda what happens along asymptotes, when you think about it.) You might be interested in studying Projective Geometry, which adds a "line at infinity" to the standard Euclidean plane; this broader context helps unify all the conic sections into a single kind of curve that has various different relations to that line. (The parabola, in particular, has its "second vertex" on that line.)
I wish to express my sincere thanks to @Blue and @amd for clearing my doubt in the comments.
The location of the focus, vertex, and directrix of a conic can be easily determined by knowing some basics about Dandelin Spheres. Wikipedia gives the following explanation:
In geometry, the Dandelin spheres are one or two spheres that are tangent both to a plane and to a cone that intersects the plane. The intersection of the cone and the plane is a conic section, and the point at which either sphere touches the plane is a focus of the conic section, so the Dandelin spheres are also sometimes called focal spheres.
In the above diagram, the yellow plane cuts the blue cone forming an ellipse. Next, imagine inserting two spheres of maximum volume in the upper and lower parts of the cone demarcated by the slicing plane, such that they just touch the surfaces (curved surface of the cone and slicing plane) but don't peep out. These two are called as Dandelin spheres. The points at which these spheres touch the yellow plane (slicing plane), $F_1$ and $F_2$ are the foci of the ellipse. So now, we have located the foci of the ellipse.
The same Dandelin Spheres are helpful in determining the directrix and the vertex. The two spheres in the above diagram, touch the curved surface of the cone in a circle (represented by white circles $k_1$ and $k_2$. Let us consider, two planes passing through these two circles separately. These planes meet the yellow plane (slicing plane) in straight lines (unless and until the yellow plane cuts out a circle in the cone, when it's parallel to the base of cone). The two lines formed by the intersection of the three planes (slicing plane, and the two planes through the two circles) are parallel to each other. These lines are the directrices of the ellipse.
The above [.gif] explains the same visually. In this, the light blue plane is the slicing plane, orange sphere is one of the Dandelin spheres, transparent planes are those which pass through the circular region formed by the intersection of the spheres and the curved surface of the cone. Here the slicing plane, forms an ellipse which is shown by blue. The two parallel blue lines are the directrices.
Even though I've explained using ellipses, the same concept can be extended to other ellipses. For example, parabola since it has only one focus, has only one Dandelin sphere. Hyperbola has two foci in opposite nappes, so it has two such spheres in the two nappes. Using this we can determine the directrix and the focus of the conic.
Now, coming to the last part of the answer, finding the vertex. This is simple once we've found the directrix and the focus. Just draw a line perpendicular to the directrix passing though the focus. This line is the axis of the conic (and not that of the cone!). The point where axis meets the curve is the vertex.
Best Answer
The inner and outer spheres tangent internally to a cone and also to a plane intersecting the cone are called Dandelin spheres. The limit case with one such sphere gives rise to the parabola.
For all cases, the foc(us)(i) is/are the tangent point(s) of the sphere(s) to the cutting plane.
The directri(x)(ces) is/are the intersection line(s) of the plane of the conic (the cutting plane) and the plane(s) of the circle(s) of tangency of the cone and the sphere(s).
The circle (the directrix line is at infinity):
The parabola: