some questions

[Vulture]

What exactly is your question ?

You can max the rage spells you like to use. And that's even as easy as it gets and as intuitive as it gets. Just use those you prefer the most and it will be very likely that you'll be asked to upgrade them.
A general rule of thumb is: restorative spells like Time Back generate experience for the Spirit according to the level of the Troop it's cast on, the number of units restored with it, the level of the spell and/or number of charges of it removed or restored. Damaging spells of course generate experience for the spirit according to the number of kills and the level of the killed units.
Support Spells like Chargers gain experience accoring to the overall leadership cost of all enemy units still on the battlefield. That means if you cast chargers first thing in combat before anything moves you'll get the most exp for it. If you do it while only a handful of enemy units is still alive you get next to nothing.