I plan to go one handed, illusion, archery, light armor, alchemy, alteration, sneak, lockpicking, and pickpocket. I'm aware that's a lot but with the legendary system I can get all the perks I want.

They are still just as good. Use the alchemy to compensate for whatever damage you lose to not having beast equipment.

I've done it before. It was hard for a no magic character, but with illusion and alchemy, you'll be fine. Just make sure you take Silent Casting.

Thanks. Also, how effective would alteration be for a sneak mage?

It'd help if you were caught, but as seeing you don't want that to happen, I say not very.

I never allow smithing or enchanting for any of my characters. I am currently playing a character very similar to what you just listed there. It works fine, just adjust difficulty as needed.

but it happens so it doesn't hurt. I know that I am not always sneaking as I am out in the open of Skyrim, that is where you will get caught with your pants down. Detect life and detect undead is nice to as well as paralyze but as an alchemist you should have plenty of paralyze poisons.

The only difference between my current build and yours, OP, is I don't have pickpocket. I am enjoying it.

Thing is, I don't want to adjust difficulty.

Then don't. Just saying you may find some enemies very difficult without improving weapons, especially early on. You should still be fine though, it will be more challenging which I assume is what you want. That is why I never allow crafting for any of my characters, smithing and enchanting that is. I like Alchemy.

Well, it has its uses. I was just saying that more often than not, you're going to be sneaking and most of the spells don't really help in that regard. By all means, if you have the perks to spare put them in alteration. It wouldn't hurt, but I wouldn't consider it very high on the list of things an assassin should have.

Yeah, I guess the Alteration spells that you may use from time to time don't necessarily warrant perking.

TBH is you are an assassin and wielding the Blade of woe with high stealth, the DB armor and wielding Astrid's gloves with huge back-stab multipliers I don't think you would need any smithing at all to compensate if you play strictly assassin type missions. For anything where you have to go toe to toe then yes, smithing woud help.

I think what others may be concerned about is if you improve everything you can easily become OP and that is a legitimate concern in some situations. If your character is going up against Falmer Warmongers though blade to blade you certainly need an equalizer. Fortunately though with high sneak you can usually get behind even them, I know because I've done it with my Stealth archer.