In a Rig Veda, the word asura can be found over 100 times, in which most of the times it conveys positive sense while disparaging reference occurs only a very few.
It is generally associated with different Vedic gods:
with Agni RV 2.1.6, RV 3.3.4;
त्वमग्ने रुद्रो असुरो महो दिवस्त्वं शर्धो मारुतं पृक्ष ईशिषे ।
त्वं वातैररुणैर्यासि शंगयस्त्वं पूषा वि...
The story of Indra and Vṛtra is metaphorical as explained below.
Since you cited a quote from the Rig Veda. Therefore, in the first place, the question of Viṣṇu helping Indra has to be understood in the context of the primary sources namely Vedas and Brahmanas.
In Śatapatha Brāhmaṇa, it is stated that
वृत्रो ह वा इदं सर्वं वृत्वा शिश्ये । यदिदमन्तरेण ...
As per 3rd Canto, Chapter-3 and Verse-6 of Śrīmad-Bhāgavatam (Bhāgavata Purāṇa) the commentator says that it was due to bad association with Banasura that he became evil and was killed by the Lord himself as Krishna.
सुतं मृधे खं वपुषा ग्रसन्तं
दृष्ट्वा सुनाभोन्मथितं धरित्र्या ।
दत्त्वा तदन्त:पुरमाविवेश ॥ ६ ॥
According to Manu Smriti, the different beings falling under Sattva, have further been classified into 3 sub-categories.
Lowest category under Sattva (Manu Smriti 12.48)
Ascetics and hermits, Brāhmaṇas, celestial beings, lunar asterisms,
and Daityas represent the first state partaking of ‘Sattva.’
Middle category under Sattva (Manu Smriti 12.49)
In Hinduism, Rahu is responsible for causing eclipses, and as far as I know, Swarbhanu is one of the various names of Rahu.
Quoting from the Rahu Kavacham, which is supposedly from Mahabharata's Drona Parva:
Katim may vikata pathu, ooru may sura poojitha,
Swarbhanuni januni pathu jange may pathu jadayaha., 5
Let my hip be protected by the funny one, Let my ...
Yes, Danu was the mother of Danavas.
In Rig Veda I.32.9 Danu was mentioned as the mother of Vritra, whom Indra killed.
Then humbled was the strength of Vṛtra's mother: Indra hath cast his
deadly bolt against her. The mother was above, the son was under and
like a cow beside her calf lay Danu.