Mod priority and load order is important to any game that has official modding support. Mods generally load top to bottom (except for FO4... which does top to bottom and bottom top), so mods that are higher in the list take priority for loading.

Now what does this mean for you?

What it means is any mods that both change the same files, the one higher in the list will be loaded and not the second one. So with this, you generally want to keep Mods that effect whole systems near the top, and then mods that stuff (like monsters, heroes, skins) near the bottom. So, In general, a load order should look like this.

Below is the order in which Mods should generally be loaded.

-Patches: Any patches you made for your other mods should be highest on the list, so their adjusted files can be loaded in.
-Large Gameplay Overhauls: These mods do wide sweaping changes to the games systems.
-Small Gameplay changes: These mods change systems but not to the extent of the larger mods above. These tend to focus on a smaller area then a larger one (like more stacking of items).
-Rebalance mods: Mods that change existing heroes, monsters, or effects.
-Mods that add stuff: If these mods are done correctly, they won't edit any of the base files and thus will never coflict with other files. These are new Heroes, Monsters, quirks, ect.
-Skins: Skins will generally only conflect with themselves, see below for a list of skins and the lettering used to try to determin what order you want your skins in.

Examples of Each catagory

-Patches: Inventory Expansion The Hell Patch, Inventory Expansion Mod Classes Patch, PBD Flagellant Patch, PBD Districts Patch

-Large Gameplay Overhauls: Pitch Black Dungeon, Inventory Expansion

-Small Gameplay Changes: Inventory Stack, The Hell, Better Trinkets, 3 trinkets, Trinket Overhaul Project

-Rebalance mods: Reduced Crimson Curse Chance, Better Stage Coach, All the Unchained Class mods

-Mods that add stuff: Ronin, Time Mage, Black Mage, Assassin, Army of bones, Bloodsucker ring, House full of piggies, Vampiress

-Skins: Unofficial Skin expansion, Crusader with a Cleaver, 3+1 Darksouls and Bloodborne.

There are a lot of Skin mods out there. Both here on steam and on the Nexus. Below are the files they use. Now you can go in and edit the nexus Files when adding them to your heroes folder so there won't be any incompabilities.

Unofficial Pallet expansion
-Abomination C, E, F, G, H, I
-Antiquarian B, C, D, E, F G, H, I
-Arbalist B, C, D, E, F,G, H, I
-Bounty Hunter E, F, G, H, I
-Crusader E, F, G, H, I
-Grave Robber E, F, G, H, I
-Hellion B, C, D, E, F, G, H, I
-Highway Man E, F, G, H, I
-Houndmaster E, F, G, H, I
-Jester E, F, G, H, I
-Leper B, C, D, E, F, G, H, I
-MaA E, F, G, H, I
-Occultist E, F, G, H, I
-Plague Doctor C, E, F, G, H, I
-Vastal B, C, E, F, G, H, I

3+1 Darksouls and Bloodborne
-Crusader W
-Highway W
-MaA W
-Vastel L

Geralt, bounty hunter skins
-Bounty Hunter W

Mysteria
-Occultist X

Waring Antiquarian
-Antiquarian J, K

(Nexus skins below)
Blue Abomination
-Abomination E, F

Backless and Bloody
-Plague Doctor E, F

Blond Vestal and Alluring Grave robber
-Grave Robber E
-Vastel F

Blue and Silver outfits
-Antiquarian L
-Cruasder L
-Grave Robber L
-Jester L
-Leper L
-MaA L
-Occultist L
-Vastel L

Brigand Highwayman
-Highwayman E

Female Crusader
-Crusader L

Female Occultist
-Occultist E

Leper Raider
-Leper K

Scarecrow Grave robber
-Grave Robber K

Shadow Dancer
-Grave Robber A