Is shikantaza meant to spontaneously relax you, unlike ch'an meditation? Is shikantaza meant to spontaneously relax you, unlike ch'an meditation? I've never taken classes in the former, but the latter seems to teach you to relax -- and then follow the breath spontaneously.
Is this about right?
To stay alert, in zazen, I focus on the tip of my nose, as and when I need to. If my thoughts bother me, I mentally turn toward them (both literally and metaphorically).
I believe that is still zazen?
I don't have any other questions about how to meditate, anymore; though I'm unsure what enlightenment or jhana is.
To sit in zazen is to sit facing emptiness.  M H's answer is absolutely correct, but like most things in Zen there is more to the story once your practice deepens.  Relaxation and concentration on a focal point have their place, but really what zazen is after is the arousal of mushin or &quot;no-mind&quot;.  In early Zen, and later in Soto, they sat in pi-kuan or wall gazing.  You'd literally just sit facing a wall.  No fancy techniques, no mantras, kasinas, or even the breath.  Just you, your cushion, and a surface staring back at you.  As you advanced in your sitting, little by little, things began to fall away.  (In fact, if you don't allow them to, you will drive yourself batty doing this practice.)  As that is happening, concurrently, you'll also begin to internalize that blank wall.  This happens through no effort of your own.  As you let go of you, emptiness is revealed.  Eventually you become the blankness - mushin - itself.  The wall becomes secondary if not entirely ancillary.
So don't worry about your thoughts, don't worry about the tip of your nose, and certainly don't worry about spontaneity.  Just sit and don't move.  Stare at the wall and see what happens.