1) yes
2) only for your own character, as for other NPCs, either you find them wearing the clothing or trigger specific scenes in which they are forced to wear outfit.
3)When starting a new game you can sometime own the clothing, but for the most part you can buy them.
4) Male & female/Futa are the the only "two" restrictions. No cross dressing.
PS
If you want, you can add this file to you lifeplay folder.
Then "While Playing" if you press [`] (next to the [1] key & under [Esc]) and enter " Change_Uniform " you can change your companion's outfit.