>>375303554
here's my experience as a user and an extremely amateur avatar kitbasher

>Are world creation commissions too saturated of a field to throw my hat into the ring?
Nope, you'll always find more
>Would it be uncouth to use store-bought assets?
Nope, most people steal assets.
>If not, would it be uncouth to include the cost of the purchased asset(s) as part of the commission cost?
Depends on who you're selling it to. If it's some vtuber who is doing this for twitch, then yes. If not, then you're going to have a hard sell because most of the audience for custom worlds are usually people doing events or RPers. RPers typically rip things off on the regular and people doing events are usually furries who have infinite wells of money.