1
The number 7 has a significance important to the seers of the Rig Veda.
Rig Veda mentions:
Sapta Rishis (Seven ages; also in the sky as Ursa Major constellation)
Sapta Sindhu (Seven Rivers in Punjab)
Seven horses of sun
Seven mouths of Brihaspati
Seven priests at the sacrifice
Seven holy places
Seven castles of the aerial demons destroyed by indra
Seven holy ...
1
No, Bhagwan Bhairava is not the prior form of Bhagwan Shiva.
The word pūrṇarūpo means complete form not prior form. And here it is said that Lord Bhairava is the complete raudra form of Lord Shankara (viz NilaLohita/Rudra not Lord Shiva).
Shiva Maha Purana 3.8.:
Nandīśvara said:
44. O sage, on hearing the haughty words of the lotus-born Brahmā, Śiva became ...
Only top voted, non community-wiki answers of a minimum length are eligible