1) When a weapon with a secondary mode based on energy (like heat, cold or electricity) deal damages, we deal damages with this secondary mode instead of the primary one. If a character with a complete immunity to heat but with no armor receive damages based on that kind of energy with a flaming sword (i.e). He will receive less or no damages at all because of the immunity to heat...but a blade is still a blade ? So is it possible for this immuned character to receive damages based on the primary mode of the weapon ?
The blade is still a blade, but it should depend if the "kind" of attack style the attacker is using. I mean, is you want to use the secondary Attack Type of a flaming sword and, therefore, attack using "fire", you are focusing in using the flames of the sword instead the blade. Therefore, someone immune to fire should not receive its damage.
Anyway, and this is a "house-rule", I would still apply half the damage of a physical "fire" attack, like that "fire sword".
2) What is the meaning of Quality of Flight ? When a character can fly, is it automatic ? Does this quality affect speed, or height,... (and how) ?
You mean Flight Speed Value? In that case, that is the speed he can "move" thought the air. It is equal to his Movement Speed Value.
3) About rounding numbers...
If I have a 8 in Strength and I receive psychic power to augment strength by 5, what will be my strength ?
Since all the augment over 10 are halved, and you need 2 points to get a +1, you would have Strength 11.
4) When I make a roll,the result must be "strictly more" or "strictly less" instead of "equal or more" or "equal or less" if it's not mentioned otherwise?
Sorry, I don't undertand this question.
5) When I want to break an objet, I need to make a roll of breaking(?) higher than the solidity of that object. So I have two long swords clashing there is no way for each other to break the other (Breaking : 3; Solidity : 13), the only way to break each other is to use the bonus given by a higher strength ?
Yes; it is more or less stated that normal swords hold by "low" strength people are not usually able to break themselves.
6) About Invulnerability...What are the damages deal when these damages get over the Invulnerability ? The full damages or the resulting difference ?
What about the damages deal against an object of Invulnerability 60
with 40 damages ?
Invulnerability? I suppose you are referring to Damage Resistance.
In that case, it is always the Base Damage of the Attack.
For example, something with a Damage Resistance of 40 would ignore any attack with a BASE DAMAGE of 35 or less.
I mean… a simple dagger used by a normal man would never be able to cut a metal wall ^^.
7) About Group of Weapons :
If I take a group of weapons (like ninja or gladiator), can I still have a weapon of my choice out of this group when I create my character ?
Sure; why not? You are paying its value in PD as an additional knowledge ^_^
8 ) About Tao :
Somewhere in the book (sorry can't remember where), it's written that Tao must have barehands as a starting weapon ? If I don't take barehands, will I still received Martial Arts at a reduced cost ?
I don't think that in any place of the book it is established that any Category, including the Tao, "must" use a weapon as an established one.
Of course, you can use any weapon that you want instead "barehands".
I hope I was of some help ^^