Spawnkilling will never be allowed, and you will keep the red Just Spawned text in your HUD. You can use that for reports.
Just Spawned was only necessary during wars because it was shoot-on-sight, right now people just use the Just Spawned tag to gain advantages, thinking they can provoke and then no-one can shoot them.
I strongly believe woot made faction members able to /engine vehicles.

If not, post a bug report when the update is live.
The increased slots will only be used on rare occurances. You can't just earn them.