in fallout 1 and 2 i didn't add (or remove) any points to my perception: what is the result of this and for what do you need perception?

Perception makes your aim better at longer distances and increases your turn sequence. So not increasing it will affect how well you hit things(won't matter if your melee) and how fast you get your turn in the fight and how often. If you had a high perception and a high turn sequence you can actually have mulitple turns before some of the enemys can have their turn.

is 5 perception bad if you're melee+ ranged (mostly shotgun)?

The result: You created a character with average perception.
Perception affects sequence which decides who attacks first in the combat rounds after the first.
Perception also affects the chance to hit with ranged attacks. (You have to spend less skill points for the ranged weapon types to get a 95 chance to hit.)
With high perception can also notice certain things in FO2.
Some perks have a perception requirement.
If you suffer eye damage your perception drops to 1.

ok, thanks to my 7 agility i can do a lot as soon as it is my turn

Just curious but what are your other stats and skills like?