I'm writing a paper for a class about the subject and honestly, I have plenty of books on the subject. The purpose of this post if two-fold. 1) I was wondering what Historians' general account of it are like, and 2) I am having special trouble finding any Journals or articles about the subject so if any Historians could point me in the right direction in that regard it would be highly appreciated.
The main thing I am focusing on is the nature of the relationship between the Arab/Berber conquerors of this period and the two major ethnic groups of Iberia at the time: the Hispano-Romans and the Visigoths. How did the two groups view each other. Was there animosity? Rebellion? How effective were the Arabs at conversion and finally what were the major effects that this had which we can still see today in Spain and Portugal?
So I've never answered a question before, but hopefully I follow all the rules. Bear with me :D
Under the Caliphate, anyone who did not follow the Muslim faith was considered a second class citizen. For a time, they were restricted from holding political or military positions and were forced to pay a "jizyah", a sort of tax. This mainly included the Christians and the Jews as they were the largest religious minorities under the Caliphate. While Christian -> Muslim conversion was widespread, the Jewish population was much less likely to convert. Under Arab rule, the Jewish peoples thrived due to the introduction of a lingua franca, and a pan-Arab nation that connected their previously isolated communities. I hope that answers your question regarding how effective the Arabs were at conversion.
Because the two ethnic groups you mentioned were largely Christian, the Caliphate's treatment of them would've mainly depended on whether or not they chose to convert. Converts were typically treated as equals and were known as "Mozarabs".
Followers of Abrahamic non-Islamic religions are referred to as "dhimmis" or "people of the book" and are protected from direct persecution by the Quran. This meant that while the Christian population would not have enjoyed equal rights, they would've lived in relative peace and safety. Therefore, the Hispano-Romans and Visigoths had 3 realistic options; conversion to Islam, remain Christian and remain under Muslim rule or remain Christian and emigrate north.
I can't answer anything regarding the major effects that this had on what we see today in Spain and Portugal.
Sources:
Albert Hourani - History of the Arab Peoples
Maria Rosa Menocal - The Ornament of the World
David J. Wasserstein - Islamisation and the conversion of the Jews
Ibn 'Abdūn Manual (Translated from Arabic by Bernard Lewis) - Market Regulations in Muslim Seville
Think of yourself as a detective. Instead of seeking The One Answer Already Assembled, you must find pieces of evidence: bits of the of the past and pieces of historical scholarship, to build your "case."
If you truly have plenty of books on the subject, and they are good academic books, you will find the evidence to build answers to both your questions in them!
First, historians are the authors of those books, so reading the books will let you know what those particular historians think. If you're lucky, the introduction or even some of the chapters will also directly discuss what other historians have thought of the topic.
Second, the back of the book should have a bibliography. In it, you will find many other books and, yup, journal articles. Look at the titles. Which ones look like they might offer good evidence to help you build your case?