where to beging at the start....
what do you want to do? Do you want to draw fantasy, buildings, paint, what area....
look at all the tools you will need for that area and focus on the fundementals.
Say it is superheroes, ok you need to know anatomy
once you get the hang of anatomy you need to focus on design for costumes etc ....
then they are going to have to have somewhere to hang out and fight evil... ok backgrounds so you need perspective to create somewhere with depth
this a broad overview of one example
as for the scans
when you are scanning an image you should be able to pick the resolution
300dpi is print quality
180dpi in between
and 72 dpi is web quality- use this one for posting on the web
you should be able to change the resolution in photoshop or painter. through image- size