first, welcome to .map!
1) spawns
First make sure you copied entdefs.pk3 to main
Right click on the 2d view in Radiant, select info and navigate to axis and allied spawns. they'll be labelled 'allies', 'axis', 'deathmatch', and 'intermission'.
2) .pk3 creation
A. Navigate to main/maps, Find all the files that have your map's name, copy them to the desktop somewhere.
B. Create new folders on your desktop, make a 'maps' and 'dm' (or 'obj', if your map is objective) folder on the desktop.
C. Put the files in the 'dm' folder, then put the 'dm' into the 'maps'.
D. Open PakScape and copy/paste your folders into a new .pk3 and save
for testing, you should remove your maps folder from main and put the .pk3 in it's place, to make sure your map is still accessible.
3) loadingscreen
you know, i've never actually made one. So i can't help you
