1/2 atmosphere probably is enough.
Delicate cores cant take much more,
strong cores can but it doesn't necessarily help -normal vacuum really just squeezes the extra resin out. Sometimes people accidentaly crush their cores with too much....
Squeezing the extra resin out is a good thing i believe, since the resin that comes out is needless and only adds extra weight. People are using hydraulic presses that squeeze the laminate much more than a vacuum pump ever will (even at 0 atmosphere).
So I guess you can not have to much vacuum with a wood core, but you should be carefull with the foam cores, as BWD allready mentioned.
it depends entirely on what your trying to achieve. i'd say run a small sample of your layup and test.
Also if your vacumm pressed your vaneers or plys into shape the your need enough force to bend them.
As for squeezing too much resin out. a test is again recommended. i generally bag with as much vacuum as i can get. so close as i can go to absolute zero. most of the stugg i've made recently have been solid carbon or carbon/glass i have no problem with sucking out too much resin.
find out what the ideal resing ratio is for the resin your using and aim for that. the stuff i use is 35%. So 35% of the total weight of the cloth. so if you have 100gm of cloth then you want to aim for 35gram of resin. however yourd probably mix 50% or more and then aim to suck down to 35% (if thats your ratio that is)