In the fourth chapter, Valmiki wrote that when he had started working on Ramayana, Ram was crowned. (1.4.1)

When he completed the Itihas it had 24,000 Shlokas, 500 chapters and 7 Kand including Uttar Kand. (1.4.2)

This Ramayana is also known as Paulatsyavadh. (1.4.7)

प्राप्तराज्यस्य रामस्य वाल्मीकिर्भगवानृषि:।
चकार चरितं कृत्स्नं विचित्रपदमात्मवान्।।1.4.1।।

चतुर्विंशत्सहस्राणि श्लोकानामुक्तवानृषि:।
तथा सर्गशतान्पञ्च षट्काण्डानि तथोत्तरम् ।।1.4.2।।

काव्यं रामायणं कृत्स्नं सीतायाश्चरितं महत्।
पौलस्त्यवधमित्येव चकार चरितव्रत:।।1.4.7।।

When Sage Valmiki completed the Ramayana he started thinking about the person who will be able to tell this Mahakavya to the general public with utmost accuracy.

He then looked at Kush and Luv. Kush and Luv are sons of Lord Ram who were residing in the Ashram of Sage Valmiki.

Though they were princes of Ayodhya, they were living there as common children of Sages. Both the kids were talented and experts of Gandharva Vidya which mainly deals with Music and singing.
Some details of their qualities are provided. (1.4.10)

रसैश्शृङ्गारकारुण्यहास्यवीरभयानकै:।
रौद्रादिभिश्च संयुक्तं काव्यमेतदगायताम्।।1.4.9।।

तौ तु गान्धर्वतत्त्वज्ञौ मूर्छनास्थानकोविदौ।
भ्रातरौ स्वरसम्पन्नौ गन्धर्वाविव रूपिणौ।।1.4.10।।

रूपलक्षणसम्पन्नौ मधुरस्वरभाषिणौ।
बिम्बादिवोद्धृतौ बिम्बौ रामदेहात्तथाऽपरौ।।1.4.11।।

Today, Every poetic work or creation is associated with any tone or mood.

Ramayana itself mentions that it has used different moods of Kavya wherever required.

These are Shringaar, Karun, Veer, Hasya, Raudra, bhayanak. (1.4.9)

Initially, Kush and Luv sang the Ramayana among a group of Sages and Brahmins. Any person who heard them singing Ramayana, he could not stop himself from praising them.

They received different gifts and blessings from Sages.