Currently I'm a level 24 dark elf VL assassin. I've been putting my points primarily into health and some into stamina if I get into a jam and need to hand to hand. I haven't invested anything in my mana pool and want to know if it's necessary. I don't plan on using much magic with this toon, as I haven't with my other assassin which is level 49. I just never really had a need for it except maybe heal spells. Anyways, I have most of the VL perks and don't seem to run across any mana issues as of yet but don't know if it will become an issue at higher levels.

Would it be recommended to put points into my mana pool and at this current leveling stage? or when would be the optimal point to do so? I still primarily adventure as my class build over VL. I play VL if I want to have a change of pace or run into some real trouble.

I would put 4 levels into you mana pool, because vampire lord is a magic based form. Or you could just equip items with magic regen or add magic points enchantments if you ever really need it. Now my altmer only magic character invested all his stuff into magic, so with that and enchantments I have well over a 1,000. This is good for me because they have spells that heal you 300 points in under a sec. With me having 100 health I almost never drop to the critical zone because I only have to cast a spell once and I am back to 100.

You'd better hope that you don't get hit by a Draugr Death Overlord with a Ebony Bow then. They do about 600 damage a shot to an opponent with 0 Armor Rating. Even with capped Armor Rating, they still do about 120 damage a shot. That'd be enough to 1 shot your Altmer Mage, even through Dragonhide.
Why my Argonian Mage has invested 3/4 his levels into Magicka, and 1/4 into Health. At Lvl 81, he'd have 300 Health and 700 Magicka without any buffs. With his enchanted gear on, he'd have 1,118 Magicka and +389% Fortify Magicka Regeneration (+327% total on gear, +62% from 2/2 Recovery). Necromage Vampire is just plain awesome.