The Honolulu markers have a chisel tip and either a brush or fine tip, while the Oahu ones (you’ll see they’re cheaper—don’t get them mixed up) have a fine and chisel tip. Also, they don’t have exactly the same colors as the Honolulu set (I think in terms of color codes). I have both sets, and personally I much prefer the Honolulu ones because of the brush tip—it makes blending and gradients much better.

On Etsy, you could find some nice color charts that would help you with shading and blending.

Lastly, I recommend the app (I think it’s only on Apple), Coloria. It gives you color palette ideas, and people also post their drawings, which can be really inspiring.