Welcome to OC.net, garanita!
Part of the problem may be the way you are interpreting the texts. When I was a catechumen, my priest gave a series of classes about the history of liturgy.
Protestants (of which I was one) tend to read the Bible in a vacuum. This leads to various different outlooks on what to do with tradition not spelled out in the Bible. Some would say it's up to the individual; others would say anything not authorized is prohibited; still others would say anything not prohibited is authorized. The problem with all these outlooks is that they ignore, among other things, the cultural context.
First-century people only knew liturgical worship. There was no such thing as "informal worship." For the Jews, all they knew was the Temple and its elaborate ceremonies, and the Synagogue and its liturgical structure. The pagan Greeks also had their liturgical worship.
They met in houses because the Synagogue kicked them out. This is described in the NT somewhere, maybe Acts, but I don't remember exactly. The fledgling religion was tiny, was probably considered a cult by everyone, and the Jews considered it heresy before long. There was nowhere else for them to meet. But tiny Orthodox mission churches still meet in houses, celebrating the same rites that are celebrated in the greatest cathedrals on earth, so house worship does not mean informal.
It is believed the Eucharist was indeed celebrated in the context of a full meal, much in the same vein as the Passover meal. This full meal fell out of use, it is believed, as early as the 2nd century. But regardless, the Passover meal, that the Apostles were very familiar with, is not informal; it is a structured liturgical service. A meal does not mean informal.
Part of the Synagogue worship was indeed a lot more "congregational participation". People would take turns preaching from the Moses Seat, and prophets prophecied, and so forth. (As for music, we have a strong musical tradition and welcome singers with open arms.) However, some of those spiritual gifts (prophecy, tongues, etc) died out very early, before the 2nd century.
The hierarchical structure of the Church (bishops, priests, deacons, etc.) was clearly in place by around AD 60 and the various roles came more clearly into definition. Again, these changes occurred under the Apostles' supervision and direction. Part of the point is to protect the integrity of the Church's teachings. The teaching authority flows from the bishop, and the priests and deacons are his authorized representatives. They teach on his behalf. But lay people, while they teach and serve in many ways, do not preach sermons and such.
If there was a truly "informal" period in the Church, it was very brief. Probably a decade or less. The Apostles themselves oversaw and directed the development of liturgy until St John died in AD 100, and we know from the Didache and other writings that the Church had liturgical prayer in the 1st century.
Under the Roman persecution, there were a plethora of rites—every local church probably did things differently—though the services themselves were surely liturgical. After the Edict of Milan, there was a movement to standardize the liturgies of the local churches so people and clergy could celebrate with other people. Over time, the cathedral rite of Constantinople became the standard rite used throughout the Church, and except for the Western Rite Orthodox, it remains that way.
And even outside the Orthodox Church, we can see that Christians have always retained the memory of this reality and regarded worship as liturgical. Aside from a few radical reformers, even most Protestant worship was liturgical until the past several decades. It is simply the way Christianity has always been.