So I'm rebuilding my character and save file from scratch, and I want to plan my build veeeerrry carefully to maximize the power for a roleplaying character as to make it also viable for general play.

I'm going to more-or-less be a Breton assassin/ranger type of character with an interest in cosmology, likely a Nightingale. As such, I'm going to have lots of Sneak perks, as well as the base-damage-boosters from One-Handed and Archery. Conjuration will really be my only focus for magic, and I plan to get a high level of it. Leaving some extra room after that just in case something is particularly important. Got any suggestions?

The real issue I'm having is how to distribute my Health, Magicka, and Stamina. At the moment I've got 250 Stamina, and it feels really good. Have you found any benefit from having more Stamina than this, or would any more be a waste?

I know Conjuration's highest-magicka spell comes down to about 370 or so with the right perks, but it still seems like a lot. With 250 Stamina, I'd have 850 points to distribute between Health and Magicka. What other ways are there to reduce magicka costs to spells? And can they be applied to multiple schools, such that I wouldn't have to spend huge amounts of points and perks on Magicka and other schools? (Given, I wouldn't care if they totally sapped my magicka in the process.)

I'm thinking of going 450 Health / 400 Magicka. What would you do?

Stamina is really only useful for repeated shield bashing and power attacking. I doubt you'll need it as a stealth character. You can always manage Stamina with the Respite perk (30 Restoration I believe, maybe 40) and Become Ethereal Shout. My vampire has around 150 stamina and it's seldom an issue, even during the day. So yeah, probably no need to go above 250. You also really shouldn't need to put too many points into Magicka, if all you use is Conjuration. Just enchant gear to reduce Conjuration spell cost, and pick up the perks that cut magicka use in half for each tier. By the endgame, assuming you level Enchanting with perks, you can enchant a necklace, ring, helm, and chest with -25% Conjuration spell cost apiece, meaning you can cast any conjuration spell with 0 magicka reduction. (If you also have the double enchantment perk, you can add points to One Handed and/or Archery on top of Conjuration). Seems to me that Health is the best place to focus your points.

250 feels like the sweet spot for just enough power attacking and sprinting, so it sounds like I should be satisfied with it on the whole. May even consider using that Light Armor perk for higher stamina regeneration. (I used the Oghma exploit to get back up to my old level, but I saved at the point where I still had a low Stamina. Might even keep it lower and only raise it after some experimentation.)
I was indeed thinking of doing Enchanting, so that should help out. What's the enchantment called that lowers spell cost? Fortify magic-school-name?

It sounds like if I abuse Enchanting, I should be able to at least reasonably well lower the costs of other schools as well. I would indeed like to at least have access to high-level spells from other schools, even if I stink at them. I suppose my Magicka amount depends entirely on just how far down I can get all of those.

Yeah, the enchantment is "Fortify ". You could consider making your enchantments looking something like:

Helm/Hood: 25% Fortify Conjuration, 25% Fortify Illusion
Robes/Clothes/Armor: 25% Fortify Conjuration, 25% Fortify Illusion
Gauntles/Gloves: 25% Fortify Conjuration, 25% Fortify Alteration
Boots: 25% Fortify Conjuration, 25% Fortify Alteration
Ring: Fortify Magicka Regen 62%, Fortify One Handed 40%
Necklace: Fortify Magicka Regen 62%, Fortify Archery 25%

That would stack up as follows:
- Fortify Conjuration 100% = 0 Magicka cost for all conjuration spells
- Fortify Alteration 50% = 50% Magicka cost for all alteration spells (in addition to perks and skill decreases)
- Fortify Illusion 50% = 50% Magicka cost for all alteration spells (in addition to perks and skill decreases)
- Fortify Magicka regen 124% = magicka regenerates 2.24x faster
- Fortify One handed 40% = One Handed weapons do 40% more damage
- Fortify Archery 25% = Bows do 25% more damage

Or some variation of this, replacing schools and enchantments as you see fit. Basically this would allow you to cast expert/master level Illusion and Alteration spells for probably <100 Magicka, and your magicka would regenrate much more quickly. You'd also be able to cast Conjuration spells for free. And you get buffed One Handed and Archery as well. You could play with different enchantments of course, but I think the key thing is that 100 Enchanting with perks is a very, VERY useful asset.

Hot damn, I love this game. I'll still get a bunch of Conjuration perks for the summoning powers and such, and I'll likely only focus on one magic school at a time.

Maaay consider going a little Illusion for the stealth casting, if I can manage it with the other trees.