The tl;dr version is to bring in some familiar elements as hooks and reference points, identify early what people can and can't do, and reveal relevant information as you go rather than info-dumping from the get-go. 

Backstory is solved by giving people the present situation, and explaining the more in-depth why as you go. I don't open an interest check to read how your universe was created, just tell me about the on-going conflict.

The main debate I think is the tools and puzzle pieces you give to a player to start with. If you have an octopus/flamingo hybrid race that possesses a pseudo-hivemind and lives exclusively in communities of fifteen... Well, good luck finding players to play it right without at least a small info dump. Which is something I'm afraid you can only pull off in advance and some 'high-casual.' Taking Brovo's Legend of Renalta, or Kadeaux' nation engines for example; that would just not work anywhere but advanced. For the one and sole reason that advanced as a stereotype, has less eye for instant gratification and gets a lot more joy from crafting and creating. Whereas the casual stereotype generally has a shorter attention span and as such both desires and provides smaller chunks of information because they generally value the interaction-parts of their posts far more. How much info you dump depends on your intended audience. The general rule is that the 'lower' the section, the less info-dump you want.

The broader your audience the more important accessibility becomes. This is why you start playing megaman with just shooting lemons instead of a full arsenal. Start simple and allow players more tools as the RP advances and new elements are introduced. Perhaps your guy's sword is infused with magic from the blessing of the elf queen for saving her from bandits. Perhaps you can create a new character of said octopus/flamingo lovechild race after some interactions with their culture. etc. This goes even for advanced, which is fairly important to note. Gaining new elements and tools to play with also encourages a sense of progression, be these elements story- (applicable IC knowledge) or game elements (you sword now shoots fire.)

Though really, progression is mostly important for holding up an RP. When it comes to fandoms vs. original, he main issue is getting interest.