Answer
The question of what method of sadhana one should follow must be determined from ancient and authoritative scriptures alone. That alone is safe.
There are many streams of sadhana, and each stream has its own scriptures, composed by such Rishis or saints who were perfected beings, whose sadhana was of the highest order, and to whom the methods of sadhana were "revealed" by divine powers.
Therefore, if you wish to succeed in sadhana and do not wish to invite calamities, you must consult the ancient and authoritative (universally accepted) scriptures of each sadhana tradition. If the scriptures are not available, you should certainly seek counsel from scholars who are well-versed in or deeply knowledgeable about those scriptures.
The Guru tradition was established precisely because Gurus possessed knowledge of the scriptures and themselves practiced sadhana. That is why they guided their disciples, enabling the disciples to make excellent spiritual progress in their practice. I do not mean to say that in the modern age there is no perfected person or no one with scriptural knowledge. However, such people are very few today.
Therefore, I consider it appropriate to follow the ancient scriptures in every sadhana tradition.
If you wish to follow the Vedic stream, it is essential to take guidance from Vedic scriptures regarding the Vedic tradition; otherwise, if Vedic mantras or Vedic methods of worship are employed contrary to the ancient established principles, calamity can result -- this is a well-established belief.
In Vedic literature it is repeatedly stated that if the pronunciation of Vedic mantras goes wrong, adverse results follow. And the pronunciation of Vedic mantras is neither natural nor easy. Many rules and prohibitions are also attached to them. Full observance of these rules and prohibitions is also essential. That is why, after the Vedas, the Puranas provided Pauranic mantras, which did not carry the dangers associated with the pronunciation of Vedic mantras, nor were there such strict rules and prohibitions as were attached to the Vedic method of worship. For this reason, after the initial few thousand years, when the Puranas began to be composed after the Vedas, the use of Vedic yajnas and Vedic mantras greatly declined, because the Vedic system of worship revolved around fire rituals (Agni Yajnas). In the Vedic method of worship or the Vedic way of life, you are required to perform Sandhya twice every day, and in that Sandhya, not only must you chant Gayatri and so on, but you must also perform Agnihotra both times -- that is, you must perform a fire sacrifice. This is clearly written in the Manusmriti.
I will try to send you photographs of the relevant pages tomorrow. For the Vedic method of worship, the Manusmriti is an authoritative text. Performing Agnihotra twice every day is neither practical nor feasible in modern life. It produces smoke that can contribute to global warming, although a portion of that smoke also purifies atmospheric pollution.
Therefore, wise scholars and saints advise turning to those systems of worship that do not require fire rituals, since these are also expensive. That is why in the Pauranic system of sadhana, performing havan and such rites is not mandatory.
Thus, in my view, you should not enter the Vedic system of worship unless you adopt the Vedic way of life.
Another point is that in the Vedic system of worship, it is the Devatas (deities) who are worshipped, not Ishvara (the Supreme Lord). Moksha cannot be granted by the Devatas. Only Ishvara can grant it. In the Vedas, and even in the eleven principal Upanishads, the ultimate destination of human life is Svarga (heaven). The emphasis everywhere is on Svarga alone. In one or two Upanishads, something beyond Svarga is also discussed, but the concepts of Nirvana and Moksha have not been clearly developed there. Vedic scholars will immediately object to this, but I have evidence for it -- I have written detailed articles on this subject based on my own extensive study of the eleven Upanishads.
The Puranas, and later the Bhagavad Gita as well, made it clear that Svarga is the ultimate destination of those given to sense-enjoyment, and that from Svarga one must return to the cycle of life and death. In the Puranas, the lokas above Svarga -- especially the four lokas: Mahar Loka, Jana Loka, Tapa Loka, and Brahma Loka -- are described as being of greater importance than Svarga. All sannyasis and ascetics who do not attain Vaikuntha or Brahma Nirvana go to those lokas. In the Vedic corpus, the fundamental problem of human existence -- suffering -- receives comparatively less attention.
Our worship and way of life should be such that the sufferings of this life are destroyed and, after death, all suffering is destroyed for all time -- which is possible only through Moksha or Nirvana. The Puranas gave some attention to this, and the Gita gave the greatest attention of all. If you understand these matters thoroughly and deeply, then further guidance can be given to you.
Regarding the daily recitation of Pranava (Om), please study the Manusmriti and similar texts, and practice it only while observing the necessary rules. The methods of performing Sandhya are also given in the Manusmriti. I will send you photographs of the relevant portions tomorrow. If you chant other names of Ishvara in place of Pranava, then strict observance of rules and prohibitions is not required. The fruit obtained is no less than that of chanting Pranava.
If all of you devotees wish to use this group for the building of your life and for attaining a good rebirth after death, or for reaching Svarga, or the lokas above it, or for attaining Moksha, then do ask questions, and be sure to bring these three scriptures into your home: the Bhagavad Gita, the Ramcharitmanas, and the Bhagavata Maha Purana.
Otherwise, do not consider yourself serious about spirituality, and do not expect great benefit.