If all you install are mods with ESP / ESM / ESL and BSA files, then install order does not matter at all. Install order matters with loose files as there can be only one version of a file in the data folder. This statement is true for any manually installed mod as well as any mod manager that does not utilize some form of virtual file management.
With the above in mind each installed loose file mod can overwrite files from a previously installed mod. Without careful planning mistakes can happen and files used in an undesired order. The correction is to uninstall the offending mods and re-install them. If any other mod also conflicts then those mods would also need to be uninstalled and reinstalled.
Mod A - a nude body mod
Mod B - an robe replacer mod
Mod C - a game wide replacer mod of all playable outfits which includes underwear and robes.
All three are loose files with no need for a plugin
A and B can be installed in any order as they do not conflict. If C is installed after it will replace files found in both A and B. This may or may not be desired. If the nude part is wanted, then A must come after C. If the looks of the robe replacer are wanted, then B must come after C as well.
Install order is the order in which loose files are applied to the data folder so that the desired loose files are used by the game
Load order is the order in which plugins and their associated BSA files are referenced by the game engine so that the desired records are used by the game.
While installation must come before defining the load order, the installation order may be affected by the load order. This is true when there are desired files packed inside BSAs. In cases like that the offending loose files need to be manually deleted so that the BSA packed version can be used.
I hope that clears things up a little bit.