The issue of where the Romanians came from (and where the Romanian language came from) is a very complicated and, at times, emotional topic.This is the sort of thing that, in my opinion, is best left to experts to mull and research, though, of course I can fully appreciate and respect your interest.There are many viable theories, and most likely we will never have a conclusive answer or a single simple answer, for that matter.Putting forward ideas or suggestions in a forum like this is likely to create ill feelings, confusion, or even misinformation, in my opinion.This is like asking a Southerner a question about the causes of the U. S. Civil War.
If you are interested in reading about this topic, there are several works in English to consider:
Ligia Barzu's Continuity of the Romanian People's Material and Spirtual Production in the Territory of Former Dacia offers what had been the official position of the Romanian government prior to the 1989 Revolution.
G. E. F. Chilver's A Historical Commentary on Tacitus' Histories I and II are worth a look.
Mircea Eliade wrote Zalmoxis:The Vanishing God:Comparative Studies in Religions and Folklore of Dacia and Eastern Europe, which might be interesting for you.
Elemer Illyes's Ethnic Continuity in the Carpatho-Daunbian Areas is another widely read work on the topic.
Nicolae Iorga, the "grand old man" of Romanian history, wrote A History of Roumania:Land, People, Civilisation in 1970.It's a classic and a good starting point.
Frank Lepper's work on Trajan's column is also interesting.
Paul MacKendrick wrote The Dacian Stones Speak, which is more of an archeological reference to the topic and part of his outstanding series on Europe.
Theodor Mommsen's Foreign Sources and Testimonies about the Forebears of the Romanian People:Collection of Texts is somewhat dry by all standards but reinforces with sources Barzu's positions.
Andrei Otetea's work is also a good starting point.He authored A Concise History of Romania in 1985.
Vasile Parvan's work An Outline of the Early Civilizations of the Carpatho-Danubian Countries deals extensively with the questions that you're asking.
Lino Rossi has a book on Trajan's Column and the Dacian Wars.
The famous R. W. Seton-Watson wrote the now-dated but important work A History of the Roumanians from Roman Times to the Completion of Unity.It offers a historical starting point on some of the issues at hand.
Victor Spinei is a leading scholar on the history of the Moldavia region.
Kurt Treptow wrote A History of Romania, which offers a good solid review.
I'd like to add that these are just the works in English (which I've put in alpha. order) that you're likely to find in a major university library.There are many other works on the matter, in English, Romanian, and Hungarian, which are important.I don't mean to suggest that these works offer the last words on the subject.In fact, it is the reverse.This is merely the starting point.But, again, it is a matter of taste to some extent.Each of these authors has an agenda, like all historians, and there are very wide degrees of quality, accuracy, and research levels to these works.