Both kinds of spells seem like great uses for both Defensive Spells and Ambush-Trap spells.
One interesting decision will be wether to use an Initial Investment of Mana, a Permanent Investment of mana, or a *pull from reserves* motiff.
Initial investment of mana is very powerful, as you would be able to set up an infinite amount of defensive and Trap-related spells as long as you have enough turns to sit around and cast them, with no other current use of your mana.
Permanent Investment seems like the most costly, which is *essentially* a temporary use of essence until the spell is triggered or activated. I say essentially because of course no actual essence is used, and that mana is once again accessible after the spell is *finally* triggered. Of course at any time you could *dispel* the defense or trap, which would free the mana for you upon the next turn. There would be some Special Case reason to use a Permanent Mana Investment, or the spell would need to be stronger, or its the only way to pay for certain really powerful Defensive or other Constant-Effect spells. (for instance, like the different Activatable "modes" in Dragon Age, that require a certain amount of stamina burn to keep active)
Reserve is an interesting system as it is Used when its needed, but if you set up TOO many of these devices, and they are all used up, then you will find yourself without any mana. Seems like an interesting, and perhaps most common application of the way to pay Mana for *Pre-Emptive* or *Pre-Cast* Trigger-spells. In general, these would draw from the Channeler's mana when needed, and if no mana is available they would simply lie dormant and not activate *yet*.
The only place to *really* go crazy on Reserve spells is on the defense of your Channeler against any and all ailment. For the rest of the cases you would only place such spells where they are Prudent and Strategically advantageous. It would not be prudent to spam reserve spells willy-nilly to aggravate rivals and opponents, as you could find yourself running out of mana at an unfortunate time for perhaps no True tactical or Strategic gain. Most likely Defensive Casters and Trickster Casters would be the most likely to pay for most of their spells in a Reserve way.
Combat casters would most likely use Reserve Defensive Spells and Permanent Investment Buff/DeBuff spells, and use on-command attack spells with wisdom, prudence, and strategy. Alot of magic wielding will rely on reading your opponent on what sort of spells they will likely be able to use, and where best to invest your mana.