Hi Jackson,
The odd experiences in concentration which you mention are familiar to me: quaking, heat and chilling, vertigious but non-nauseating spiralling, disproportion in limbs, images of objects, faces looking at me, and once, startlingly, a figure pointing at my nose and sniggering while I tried to concentrate on the breath

In research about such experiences, I found some teachings by a Thai forst Master (Ven. Ajahn Fuang) - see http://www.accesstoinsight.org/lib/thai/fuang/itself.html#vision
As to the body sensations - I sometimes try to leave them alone by concentrating harder on the object, sometimes I switch to investigation at that point, depending on what I set out to do. I always "plan" my meditation beforehand: set a timer, and decide wheter to do pure concentration or concentration first and then insight.
Cheers,
Florian