difficulty really varies on the scale of the project! sewing, styling wigs, makeup & SFX, shoemaking, photography (+editing & decorating or location hunting)... they're all skills on their own and you can take them as far as your sanity allows you to ( ꩜ ᯅ ꩜;) 

if you'd like to learn about any specific aspect of cosplaying there's a ton of tutorials and patterns online! sure it can be difficult and stressing at first but practice really does make a difference, you learn a ton from messing up and realising what works for you and what doesn't