Sprite formats, and so on

I'm just starting to get into the nitty gritty of fiddling around with Essentials, various plugins and so on.

The downside is, I have no idea how to organise sprite sheets; be it back sprites, overworld sprites, and so on.

So I was wondering whether there was a standardised size for each given type of sprite. Like, how many pixels must a back sprite be to function in a Heartgold-type game, and then a Black or White style game, and so on?

I've been looking for tutorials, but I'm utterly confounded in what to search. When I search for sprite sheets for many characters, I can't really make sense of them, nor figure out how to divide them up into functional sheets.

There's really not too many tutorials out there for stuff like that because I think the easy thing to do is simply rip sprites that are already implemented in Essentials and use those dimensions to guide the organization of your sprite sheets. Off the top of my head I'm relatively sure HGSS sprites are 64x64 but it's not a completely hard-nosed requirement.

As far as overworld sprites, though, that's something I wonder myself as I develop my own game. So far I haven't been able to figure out exactly any standardized dimensions for them, although I'm sure they exist, so I've resorted to the most utterly basic problem solving strategy of trial and error. Again, ripping sprite sheets already in Essentials helps. Even further, there are a lot of BW/HGSS overworld sprite sheets already formatted for Essentials on various websites on the internet, like Deviantart. I'd suggest searching for some and using those as a baseline.

Hope that somewhat helped.