Raven provided us with a couple of the maps uncompiled for us to look at...
Kejim Post (first SP mission) is about 8000 by 9000 map units.
It is a little under 4 megs un-compiled.
ctf_bespin is about 3,000 by 8000 map units
and the .map file is 1.5 megs aprox.
not shure what kind of size exactly you are talking about but there are both i can think of.
I have a little (60k byte .map size) I made from Rich's tutorials, it compiles
in about a min and a half...it about big enough for a two person deathmatch.
ctf_bespin took about 7 min to compile on my computer.
yes you can do SP maps
I dont know how to do objectives yet either...
I'm not even shure there is an objective system per say, it might all just be
Hope some of that helps you