You have many questions and let me answer each question. Actually, most of your questons are answered already on this site. As it is difficult to mark this question as exact duplicate, i am providing an answer for this.
Is Non Veg allowed in Hinduism?
Yes. It is allowed but not recommended.
You can eat meat when your life is in danger i.e, when doctor prescribes you to eat. For example, your body may badly require some protiens and you can eat meat in those cases as Human birth is aquired after lots of good virtues or Karma. It is not wise to torment your own Human body by not eating mamsa in those cases. Also, you can eat meat if you do lots of Physical work. Rama, Krishna and Pandavas as Kshatriyas ate Mamsa. They need to participate in wars as part of their Kshatriya Dharma and they need muscular body to do that.
This answer explains beautifully, why it is not recommended (not mandatory) to eat "living animals" but not "living plants". I provide some verses from that answer to justify eating meat when our life is in danger.
One can eat meat when his life is in danger. (i.e. if the condition is
such that if you don't eat meat you will die.) [Manu. Smrt. - 5.27]
For the sustenance of life Prajapati created everything. So both
movable and immovable are the food of prana (life force) [Manu. Smrt.
- 5.28]
Actually, we should offer whatever we eat first to God or our Ista Deva. This is what Krishna Paramatma says in Bhagavadgita 3.13
yajña-śiṣṭāśinaḥ santo
mucyante sarva-kilbiṣaiḥ
bhuñjate te tv aghaḿ pāpā
ye pacanty ātma-kāraṇāt
The devotees of the Lord are released from all kinds of sins because
they eat food which is offered first for sacrifice. Others, who
prepare food for personal sense enjoyment, verily eat only sin.
So, it is clear that we can offer food to Devas or Lord first in those cases.
Also, there are three types of foods. Satvic, rajasic and Tamasic. Our Gunas or traits depend on what we eat. Generally, it is not recommended to eat Tamasic foods as we acquire Tamas guna.
Refer following questions to get more clarity. Is the ritual of killing an animal as offering to Maa Kali correct? and Should a Brahmin be vegetarian?.
Should i become Kaali Maa Bhakta to eat meat?
As said above, we can eat meat if our life is in danger or during festivals when animals are sacrificed to Kaali Mata or any form of her form (especially Grama Devata in South India).
As stated in this answer, sacrificing animals for Kali Mata or any Grama Devata will take those sacrificed animals to heaven, as mentioned in Srimad Devi Bhagavatam. But this doesn't mean you should be Kali Bhakta to eat meat. You can offer it to Devas (or your Ista Deva) and eat it (mostly recommended this only when your life is in danger).
Manumsriti says,
Irrespective of whether one has bought the meat, killed the animal
himself or has received from another person, there is no fault in
eating meat when it has been offered to the gods and the manes. [Manu
- 5.32]
You can worship any form of Brahman (Shiva, Vishnu or Durga) or any Deva and eat meat by offering to your Ista Deva.
Please refer the question, Should we chant mantras before eating food?.
And do sacrificial acts not tackle the law of Ahimsa (the rule which
states that we should not violate any living being) in Hinduism as a
whole?
Ahimsa is good but not mandatory. One should decide to choose Himsa or Ahimsa based on their Profession or Varna. A soldier can't follow Ahimsa and defend the country.
All those warriors who die in battle field by following Himsa reach heaven, as they strictly followed their (Kshatriya) Dharma or duty. This is the reason, all those warriors who died in Mahabharata War reached swarga including Kaurava Army.
This is what Lord Krishna says in Bhagavadgita 3.35,
śreyān sva-dharmo viguṇaḥ
para-dharmāt sv-anuṣṭhitāt
sva-dharme nidhanaḿ śreyaḥ
para-dharmo bhayāvahaḥ
It is far better to discharge one’s prescribed duties, even though
faultily, than another’s duties perfectly. Destruction in the course
of performing one’s own duty is better than engaging in another’s
duties, for to follow another’s path is dangerous.
Krishna Himself supported Arjuna to participate in war as it was proper to Arjuna as Kshatriya. So, choosing Himsa or Ahimsa depends on Varna or your profession.
