If I have a conjuration of 25, and I choose the Apprentice Conj costs 20% less for 25, do I still get the Novice Conj costs less perk which only needs 20? In other words, will my Novice spells not be reduced if I choose the Apprentice perk?

Not a 100% sure, but I think you have to have the novice thingy before getting the apprentice thingy. Even if you did get apprentice first, it has no effect on the novice thingy.

Each step is 50% reduction for the spell level and you have to take them in order so you'll have the reduction for novice and apprentice spells. It's a little different from weapon perks.

Poop...

If you are on the PC there's a nice mod that makes those perks give a buff to all schoools. Magnitude of effect for destruction and restortion and duration for the others. There are some other small tweaks as well. Pretty nice and modest but sensible changes to the system. I am onn my phone at the moment so I can't check the name real quick unfortunately.

There's also a mod that removes prerequisites so you can choose any perk you have the skill level for without needing the perks that come before it.