I'm actually soing my thesis on elves!
Re: origins, the most accepted theory is the one with *albho- for brightness. There's another hypothesis (actually the only theory cited in the Oxford English Dictionary, even though it's more of a stretch) that links them to Vedic deities through the word *rbhu (with a sonant r, but I'm typing from a phone). See Kazanas for a paper on the subject, I believe it was called Indo-european deities and the Rg Veda.
As for svartalfar and such: kee in mind that the main source of that classification is Snorri Sturluson, who was writing from a Christian perspective and trying to make elves more similar to angels and devils. There is no mention of dark elves in earlier Scandinavian sources.
Most early Scandinavian evidence points to elves being seen as minor deities, possibly linked to fertility and prosperity. They received some sort of sacrifice (not much detail on this in Skaldic poetry, but an "alfablót" is mentioned once and Kormaks saga talks about pouring bull's blood on a mound where elves live) AND were linked to the sun through the poetic metaphor alfrodhull (literally "elf's wheel" or "elf's glory", meaning sun. Again, missing accents here, sorry). Human warriors and kings were also described as metaphorical elves in poetry, most notably Norwegian king Olafr Geirstadhalfr "the Elf of Geirstadhir", named after his burial site, who was also sacrificed to in order to secure prosperity.
Also, the meaning of alfr (the Old Norse elf) is a lot less clear than it looks. It was probably not a "race" of beings as we might conceptualise today. More likely it had a range of meanings, possibly as wide as "any being capable of giving supernatural blessings" or at least "any semi-divine creature". Medievam folk did not have a concept of taxonomy and as such did not classify things the way we do.
In the elder Edda, elves are routinely paired with the Aesir in poetic formulae, possibly with the meaning of "all divine creatures, from gods to elves". In at least a few songs (esp. Lokasenna) they seem to be synonymous with the Vanir (Freya is said to have slept with "all Aesir and elves", which Loki says is incest, apparently because she's an elf and her brother is too?). Freyr especially is linked to the elves through Alfheimr, the elf-realm which he is said to have been gifted with. This association is however not present in other songs, where vanir and elves are mentioned side by side as though they were different groups (see for instance Skirnismal and Alvissmal).
The only elf character in the Edda may be Volundr, who is said to be alfa ljodhi (ambiguous, possibly "of the elf-people") and visi alfa (leader of the elves)in Volundarkvida. This is weird because Volundr is a very popular character with equivalents in Anglo-Saxon Weyland and German Wieland, but this is the only source calling him an elf. Here the term may have been a way to classify him as an ethnic Other (being a Sami prince) and carries implications of dangerous beauty. There's a very good paper on him, called The extreme emotional life of Volundr the Elf.
The earliest of these sources date back to the Ninth century. Note that nowhere are elves described as being specifically diminutive in size, invisible or whatever. That is likely the product of later shifts in meaning or belief, possibly linked to Christianization and merging with other supernatural beings, such as dwarves (as in the aforementioned svartalfar, which are described as being black as coal and are also apparently dwarves, at least according to Snorri), and landvaettir (nature spirits). Terry Gunnell has done a lot of work on this, check out How Elvish were the Alfar? (2007).
Anoyher good source is the work of Alaric Hall, esp. Elves in Anglo-Saxon England (2007). The book focuses on old english but also goes over Scandinavian evidence.
Might share more sources later once I get to my computer if anyone is interested.