Plants, metals, and even fade-touched metals (eventually) respawn. Leather and cloth have to be, um, collected post combat. I'm going to try to explain schematics in a way that makes sense, but crafting is really big and it really is better to learn by doing. Don't be afraid to craft anything you want out of metal. There's so much iron in Haven to give you a chance to play around and make mistakes. There are even some nugs, rams, and druffalo around to provide leather. You are going to have to go to the Hinterlands for cloth, though, and you might want to get a level or 2 under your belt before you take on a druffalo. They're not aggressive at all, but they do take a long time to die for only a little leather. Unless I have a pressing need, I usually feel I've got better things to do with my day than whack away at something that's barely aware I'm there, but will trample me if I annoy it enough. You can actually take damage in Haven to the point where you need a health potion. I did not know this.
Each class has 3 tiers of armor, and each tier is broken down into 3 different looks. The tiers carry different names, and they will help you compare if you are trying to figure out if the loot you find is better or worse than what you can craft. Tier 1 armors are scout/apprentice/defender, tier 2 are hunter/enchanter/vanguard, and tier 3 are prowler/battlemage/battlemaster. The looks are armor, coat, and mail, and they look different on each companion or the inquisitor. For the inquisitor, I've nicknamed them the cutaway coat, the duster, and the saddlebags. After the first schematic you get from Harrit, which is a trifle underpowered (but still better than the stuff you're finding,) all looks have the same actual armor class, but different properties. These properties are determined by the nature of material and its utilization.
All materials provide the same armor class by tier, so tier 1 cotton is going to protect the same as tier 1 ram leather and tier 1 iron when it comes to actual armor value. The difference comes in with regard to the extra slots. Tier 1 armor and weapons come with one slot for material bonuses, two for tier 2, and 3 for tier 3. Those material bonuses can take the form of utilitiy, offense or defense. Utility raises statistics. Rogue armor and weapons usually call for leather, and raise dex and/or cunning. Mage stuff calls for cloth and raises magic and/or willpower, and the warrior stuff uses metal to boost strength and/or constitution. Offense is used for weapons, and leather there provides critical chance, critical damage, flanking damage, or a chance to rend armor. Cloth in the offense slot gives you attack, barrier penetration, or heal on kill. Metal gives armor penetration, chance to stagger, extra damage vs. guard, or attack. Defense is what armor uses mats for. Leather can provide a chance to sunder the armor of opponents who score a hit on the wearer, ranged defense, or resistance to fire or cold. If you want electrical or magic resistance, you need cloth, though. It also can make healing more effective (raising the amount of health regained.) Except for dragonbone, most metals fare poorly in the elements, but provide protection in the form of extra health, melee defense, or a chance to stagger those foolish enough to attack the wearer.
The materials have actual statistics listed for each category, so to find out what you're getting, look at the material you intend to craft with and multiply the factor listed on the material by the number it requires. I think 4 dragonling scales provide 8% fire resistance at 2% each, for instance. All materials in the same tier will provide the same level of benefit, just in different ways. For instance ram leather provides the same level of protection against cold damage that dragonling scales do against fire. Your chance to land a critical hit may look smaller than the amount of critical damage you'll do if you just look and see that the percentage is higher for one type of leather than another, and the amount required is the same, but I think that's because critical chance has a greater impact across the whole party when you start looking at class abilities. In any event, all materials of a given tier that provide a certain type of protection will do so to the same degree.
Got all this? Now I'm going to throw in the monkey wrench and tell you about upgrades. Upgrades effectively expand the amount of stuff you're able to do with the stuff you make, like taking on extra material slots. The cool thing here is that the upgrades you craft or find can be applied to any compatible weapon or armor, including the stuff you find. If I find a suit of armor or a weapon that would be so much better than what I've got now, but it just doesn't do blank, I might be able to craft an upgrade that does. Some armor and weapons come with the upgrades built in already, and they're cool, but I like the flexibility of stuff I can add or remove as the need arises. Furthermore, all the premade armors have the same look for anyone capable of wearing it, and most have race restrictions. If you like the look and are a race that can wear it, you can craft armor that's almost as good as the stuff you can upgrade, but you'll need far fewer mats. It's a bargain, but I'd rather spend the materials to get the look and flexibility I want. Here, the thing to watch out for is the name. If it says anything but the labels I've listed above (scout/apprentice/defender etc.), it comes with built-in upgrades and may or may not be compatible with your race.
I hope this helps and I haven't bored you to death.