Let us focus on the word अक्षर. It is not the same as वर्ण. The word अक्षर which literally means imperishable, refers to the primordial energy of the universe. This is also called अमृतात्मा and षोडशी. It is one, but can become many due to interaction with the background structure. अक्षर has 9 विन्दु, whereas वर्ण has 8 विन्दु. अक्षर has वृहती छन्द, whereas वर्ण has अनुष्टुप छन्द. अक्षर is the base (प्रतिष्ठा) of वर्ण, which represents the describable physical world – hence वर्ण. Its 8 विन्दु represents what could be described as the 8 gluons (अग्निश्च जातवेदाश्च सहोजा अजिराप्रभुः वैश्वानरो नर्यापाश्च पङ्क्तिराधाश्च सप्तमः । विसर्पेऽवा अष्टमो अग्नि नाम् । एते अष्टौ वसवः क्षिता । वसयति इति वसवः). You must remember that gluons are high energy bosons. Hence they are described in the Vedas as अग्नि. Unless the gluons confine the quarks, structure formation will be imposible. Hence अनुष्टुप is said to be responsible for creation.
When अक्षर moves freely, following the Vedic principle: तीरश्चिनो विततो रश्मीरेषा, it moves in waves passing momentum only. This generates waves (कम्प) that lead to formation of sound (सरस्वति वाक्), which is expressed as वर्ण. If it moves with greater force than necessary to form a wave, it bombards on the background (चिति), which leads to consolidation as particles (आम्भृणी वाक्). Both are called वाक् because we express the concept of particles only through speech form.
In this process, when the air moves from the navel, it comes through chest, throat and after passing through the vocal chord, move out through mouth. If every part is in its normal position (संवृत), it come out as the breathing sound. If the vocal chord is stretched (विवृत), it comes out as speech (वाक्). The first sound that comes out with minimum effort is अ. Panini has shown that all other वर्ण comes out from संवृत अ to become deformations of विवृत अ. Hence his text ends as अ-अ. I am not discussing the scientific aspects related to fundamental forces of Nature. The mechanism has been elaborated in शिक्षा and प्रातिशाख्य texts. In case you want, I can explain separately.
Coming to छन्द, the first thing to remember is it is the first of five पशु । Here पशु does not mean animal, but all observables (यत् अपश्यत् तत् पशवः). During the creation phase, everything comes out from the same source in the reverse order till structure formation starts (कश्यपः पश्यको भवति । यत्सर्वं परिपश्यतीति सौक्ष्म्यात्). In order of decreasing temperature, stars are classified into seven categories as O, B, A, F, G, K, and M. Vedas call these आरोगो भ्राजः पटर पतङ्गः स्वर्णरो ज्योतिषीमान् विभासः । The galactic center is called कश्यपः. It does not move (स महामेरुं न जहाति). It expands in the big bang and takes back everything during final annihilation (यत्ते शिल्पं कश्यप रोचनावत् । ... यस्मिन्सूर्या अर्पितास्सप्त साकम् । तस्मिन् राजानमधिविश्रयेमम्). It functions like a blower (भ्रस्ताकर्मकृदिवैवम्).
Like space, छन्द covers (छादयति इति छन्दः) everything (आधारशक्तिप्रथमा सर्वसंयोगिनां मता). Similtaneously, it is the first unit of energy (quantum – प्राणमात्रा छन्दः). The other पशवः are related to the other fundamental forces of Nature. We are not discussing these here. The well known seven छन्द are related to confining energy. There are four more छन्द, which are related to confined structures: मा, प्रमा, प्रतिमा relating to fermions (ऋषयस्सप्ताऽत्रिश्च यत् । सर्वेऽत्रयो अगस्त्यश्च । अगस्त्यः कुम्भजातः) and the fourth अस्रीवय relating to bosons (दिक् देवता). All other छन्द are related to prosody – not Vedic छन्द.