Where do you know that you will have over 1000 stamina at lvl 50?
You start out with 100 in each attribute.
Each level you gain 20 in each attribute.
By level 50 you will have, at least, 1080 in each attribute.
You also gain 1 attribute point each level that you can place in an attribute of your choose.
This point will add 10 to the attribute of your choosing.
By level 50 you will get 490 points to distribute from this.
where are you getting those numbers from???Seriously I want to know, besides I didn't come up with an actual build for you to make assumptions as to what you should wear and put attribute points into. I simply wanted to explain that light armor is better for spell casting (with more magicka associated with the armor pieces) and heavy armor better for survivabilty (with higher armor and health associated with the armor pieces).If I'm wrong then why would a caster wear anything other than heavy armor in ESO (if you don't look at passives and attribute points for a minute, although they definately play a part in character building)???
Simple math? 
There is also leaked videos that showcase your attribute ratings at level 50.
Light armor is good for all builds that are fueled mainly by magicka abilities (which is ALL class abilities, not just long range "casters").
For example, you can build a perfectly viable backstabber by wearing medium armor and dual wielding. Spending stamina to sneak around. Sneak attack from behind. Channel Flurry while he is stunned from the sneak attack. Twin slashes for DD and a DoT. Trigger Evasion from medium armor to make you really hard to hit. Hidden blade if he tries to run. Spark if you need to get away. Your start class does not really matter for this build. You can be a templar, sorcerer or dragon knight. Doesn't matter. This particular build is only fueled by weapon and armor skills anyway.
But you can ALSO build a perfectly viable backstabber (more of an illusionist assassin really) by rolling a night blade wearing light armor and wield whatever weapon you like. Spending Magicka to become invisible with Shadow Cloak (rather than using sneak). Mark target and trigger haste. Open up with veiled strike (rather than sneak attack). Follow up with a power attack to exploit the off balance (to knock him down). New Shadow Cloak to open up for a new cheap shot opening. This build depend abilities that are only fueled by magicka.
Light armor and a focus on magicka is generally better for restoration staff healers and destruction staff long range users (better races for this would be altmer, breton, dunmer).
Medium armor and a focus on stamina is generally better for archers and dual wield users (better races for thsi would be redguards, khajiit, bosmer).
Heavy armor and a focus on health is generally better for One hand and Shield tanks and two handed melee range aoe builds (better races for this would be nord, argonian, orsimer).
You can also build builds that mix both class abilities AND weapon/armor abilities (or plan to utilize a lot of stamina for block, sprint, sneak, dodge...) so you take advantage of and double dip into both resources. That will is probably the most successful recipe for success if you ask me.