hi got another question about UV mapping

assume i do planar mapping for the body , how do i ensure the texture is not stretched ?

refer to pic

1) small planar map , texture nicely displayed , big on UV editor
2) large planar map , texture stretched, small on UV editor

ultimately i want to arrange all my UVs on the top right corner square for export and painting so
when i click UV layout , it arranges all my uv into the top right corner square, after which the texture on dino is stretched again

will this affect my texturing later, pretty confused here

pls pardon me for my noob question

what is the correct way of uv mapping and arranging them .
is there any hot keys?

thks