I know there are some other questions about the same topic on the forum, but I have some other questions I coulnd't find on other posts.

In the future (and I hope it is soon), when I have some better mapping skills, I'll want to start taking some of the requests on the Mapmaking Request forum, specially aiming Paid request - again, considering I'll have enough skill for this mission -, and by what I have read on most requests people usually ask for a size so that they can print it on a A3 paper, or even on a Poster, and thats where I need some help of you.

When making maps for printing purposes it is needed 300 dpi or more right? What about the pixel size? What would be the better size(px)?
Also, lets say I draw a map by hand on a A4 paper, when I "photoscan" it my camera takes the picture with 72 dpi, editing the number by PS, from 72 to 300 dpi, brings any issues to the image(except for the size grow)? I mean, does the image loses any quality?
Also, a scanned A4 paper draw would look pixelated if printed on a A3 paper?

That is it for now. I'm sorry for the great amount of questions, and if any question got a little confused,