Newbie GM here.

There's seem to be two popular styles of "Looting" in RPG. 
(I don't know if the style actually have names)

+ Style 1: "Elder Scroll" where you can loot everything down to their undergarment. If you see it, you can loot it. 
Pro: In video-game, I love this style, Skyrim made me a hoarder and I always had $.
Con: Even at 50% value some armor/weapon are valuable. Players can be rich in a short time.

+ Style 2: "JRPG" ex: FFX or Ragnarok Online. Each enemy drops a small amount of $ depend on CR and a loot table for that CR. 
Pro: Weight limit isn't really a big problem, GM can control the loot better
Con: Unpredictable loot

I'm starting a homebrew long-term campaign LVL 3-15 hopefully. 
I'm worried if allowing players to loot everything off an enemy would make them too powerful/rich too quick.
I want my player to continuously try to find more ways to make $.
-Crafting item & Sell
-Do odds jobs
-Hunting pelts
-Finding more mercenary job 

I agree with big Lizard, in D&D adventurers get their wealth from adventuring not gathering trash. Sure the players can loot the bandits underwear if they ask but they will require a good persusion roll to sell it for 1cp meanwhile ven at low levels they might get 50gold for killing the bandit.

Treasure found should fit where they find it but you can throw in a few surprises, after killing a giant spider they might find the body of a dead adventurer encased in web that the spider was going to have for its next meal, investigating the adventurers corpse might reveal they were carrying a +1 sword a gem and 30gp.  (You could also throw in a moral dilemma by them also finding who there were and where thier next of kin are).

You are playing 5E, a game that requires you the DM to watch and maintain balance of loot to give the game a challenge.  5E was designed with limited range of bonuses you can give a player without unbalancing the game, that also includes mundane items.  Allowing players to loot everything and say build a full set of ankheg plate at level 3, means they will have base AC 18 + Shield, well now AC 20 at level 3, and most monsters they are fighting will have a +4, meaning they can hit the guy 20% now.

There are various systems you can buy brom DMs Guild if you want to help with looting, but they tend to be fairly easy to gather, and your players will do it all the time to build their own magic items and eventually they will start to trivialize the game if you give them too much.

In 5E magic items should be somewhat rare if you want to go to level 20, if you only plan on going to level 5, then let the game go wild with magic items, with the understanding the game ends at level 5.  For longer campaigns, create a system where coin and XP is spent to build a magic item, whether it be permanent to a potion or scroll. Permanent item should eat up a lot of XP while potions/scrolls should be a little.  It should be set up where there is some pain on making a magic item but its something the player feels will help the campaign permanently.  If the player wants a flametounge, then put in a campaign goal to kill a Red Dragon to finish the item, because that Flametongue greatly increases a tanks DPs to the point where they can one shot CR2 and lower mobs in a single round of combat.

Thanks, everyone!  

Your right, DnD more logic base on realism a bit. 
I also notice the length of the campaign is important to note.
Shorter campaign the loot should be about rare/magic item are a bit easier to find? 
Longer Campaign is a marathon to get those rare/magic items?

The game I'm planning to run is a long campaign. Starting level 3 and ending at 10 or 15.
We're trying for a more hardcore game with the alternate rule of short rest = 1 day and long rest = 1 week.