Can the selection window be made bigger?
Sure it can and it's not even very difficult:
Mapper interface is defined in Mapper\data\mapper_default.ini, you can change position
and size of ui elements there (and their look if you change the graphics). The property
you look for is ObjWork and maybe ObjMain.
Mapper window size is the same as client resolution - you can set any width or height
by editing ScreenWidth and ScreenHeight in Client\FOnline.cfg. Make it as big as you can.
Unfortunately I don't think you can make multiple rows this way. You would have to make
your own selection window with scripts, which is "a little" more complicated.
A REALLY better way to do it would be writing an application that takes proto ids and
their graphics from all protos and makes a big image from it, but you would need a
programmer for this if you can't do it yourself
PS. While I understand how it could be useful to have a big gallery of available protos,
I'm not sure why would you need it to
plan a map. I think all you need is to know roughly
what the Mapper has to offer, then
a sketch should be IMHO sufficient. Making 1:1 mockups
from actual graphics seems to me like an overkill, you could just do the map...