I'll answer your rule queries first.
If you have a mixed line of bow and spear, the spear can countercharge or intercept but cannot start or move within 1BW from all enemy TuGs. The bow will probably not be able to shoot in the charge phase (the enemy would have to be within 1BW - in which case they might press forward into the bow defeating the point of countercharging or intercepting), but may get a shot during the shooting phase.
If you get it right, the benefits of shooting into the melee can be effective, but bear in mind that the opponent's supporting files may be contributing to the melee combat.
As the rules currently are, falling back is still an effective tactic for bowmen. It is something I would really like to see altered in a future edition (quite a few years away!) making formed bowmen more effective at slowing down opponents and not allowing them to shoot and fall back.
As regular listeners to the podcast will be aware, I am firm believer in protected bow and generally don't downgrade the quality and or shooting skill of my bowmen and crossbowmen. At the competition last weekend I did quite well with 3 TuGs of 6 protected experienced crossbow in my Aragonese army. They combined well with my knights and almogavars.
As far as Chinese armies go, I have had some success with Tang, but these use Fubing mixed units which are quite tough and work somewhat differently.