More manual trans questions

What is the purpose / function of the shift keys and their springs in the slider assembly ?

Is it to make the slider "want" to be in the neutral gate position ?

Is it to put a little extra pressure / force on the synchros when going for engagement on the gear cone ?

shift keys act as detents to hold slider in neutral position, then when you start to shift, they press against the brass rings to engage the cone of the syncro, the brass ring locks onto the cone, this speeds up or slows down the gear you will shift into, so you do not grind the syncro teeth.

I believe they also hold the slider in the gear selected ?

X2.

Otherwise, you'd have to hold the shifter and keep the forks against the synchronizer