I have plans on making a small top down rpg using unity to get acquainted with the engine. Although, I also want to make my own 2D pixel art. I have experience making sprites, and I also have experience programming. My only problem are the dimensions of which the characters, items, backgrounds should be drawn in.

I see a lot of pixel art assets that have dimensions set at 32 bit, 16 bit and 8 bit. I'm assuming that's based on the color palette. Right now I have a character drawn on Photoshop, but the dimensions are not exactly symmetrical. Is there some tutorial out there that describes the standards for every top down 2D rpg? I would like to know how many pixels each side should be for characters, and generally everything else. I am afraid if I make the character a scale different than the tiles, it'll look out of place. 

My Photoshop canvas is set up for 2D pixel art, with guidelines and grids. I am also using a 300x300 pixel canvas, so I don't know how to use the space accordingly. 

Overall, I am lost on what to follow. I don't know whether I should just keep making the characters the way I'm making them, or have them sized according the the entire tileset. If someone could guide me to a blogpost, tutorial or paper talking about this subject, I would greatly appreciate it! It's what's holding me back at the moment. I will try using free assets for now, but I plan on making my own for later.

Youtube is your friend. There are HUNDREDS of pixel art tutorials on there. Not all of them are great but still most are useful. I would do a lot of drawing and traditional sketches first. Concept out your game in full before you get into production. Also know that not every asset you create will be used. You REALLY want to create more assets than you actually use. You want to chose from a massive pool and chose the best ones rather than relying on every piece being essential. 

Also there are methods to upscaling your game to 1080 without worrying about being the right size. As long as your art has the pixel art look you're going for you'll be alright. 

Sorry I wasn't more specific. I'm actually just getting into pixel art myself, generating a one-minute pixel art intro scene for a game. Best of luck!

That depends mostly on what you want but for myself, I usually use a grid of 64X64 for characters and 32X32 fo tiles. By doing so, my characters a little bit bigger but still fits in the game. But I was using it for platformer though. So I don't know if that helps.

Also, try not resizing it when importing in Unity or when doing the Spritesheet.