If my character has like 25 karma to it's name, can I then use on 5 and one 10 karma upgarade, or switch to a 25 karma?
You could do either, they choice is up to you.
Is it so that every extra space (space 2,3 and 4) you use will cost the runner 10 karma?
So if you want a dude with all the most expensive upgrades it would cost 50+50+45+45 and the +30 for the extra spaces? Total of 220 Karma.
Can you loose karma?