Hey BROJ, I didn't see your post when I made mine. Sorry about not addressing your points. The Lavos 2nd Form room certainly does resemble a constructed facility of some sort. However, I am curious as to if you have ever seen this
computer generated animation of the inner working a single cell. Some of that resembles a constructed facility as well.
Certainly, the design of the "room" implies an artificial construct, but not definitely so. But I've already said I am biased towards a naturally occuring Lavos.
Still, Duck-footed-Lavos was wandering around inside shell-Lavos. He/it presumably had the intelligence to design and construct the room himself, though that does bring up the interesting image of Lavos building a structure inside of itself.
Faust, I highly recommend checking out Wikisource. That is actually were I've read the majority of my Lovecraft. If I might make a few suggestions, The Call of Cthulhu, The Case of Charles Dexter Ward, The Colour Out of Space, and The Unnamable are all wonderful examples of his work (and it pains me to limit myself to only four when there are so many others that are wonderful as well).
Given that Serge had the choice (Arbiter status) over how it would evolve, and that it wasn't yet capable of devourering space-time, that seems to imply that, at least not as of "yet" from the game's prespective, it was not capable of evolving ala Lavos (that is, taking the "genetic" material for a timespace and incorperating it into itself, then sending spawns to another timespace to do the same). Given more time, it might have been able to, however.
I am inclined to believe that Serge did have to unlock the TD from the DBT (specifically, by using the Time Egg to open that gate), as every other time in the game when it is mentioned the Serge destoryed the future, the particular verb tenses imply the had done something in the future.
Out of curiosity, as I don't recall, can the DBT be accessed from either world? If only homeworld, that would then seem to imply that opening the gate is what dooms the future (and given Belthasar's machinations, it was inevitable that he would open the gate).
"How" the TD would evolve seems to relate to his use of the Chrono Cross. Either it would continue evolving into a fully matured TD or he would use the CC and the course of its evolution would be different (but here I don't think we can say that this evolution is the same as standard Evolution; I suspect it is looser and more akin to just a change, not the actual process of Evolution).