3, 4, 6.
I've never heard of an Arabian fleet conquering the Philippines.
I basically think that for the last 2,000 years, monotheism has been on the rise.
I think forced conversions also happened a lot, especially in the western part of South Asia (modern day Pakistan). Of course there was more to the spread of Islam than just that. I say a combination of 2,3,4 and 5.
As for #5, low caste Hindus might have converted to Islam to escape the caste system, but they could never totally escape it.
http://en.wikipedia.org/wiki/Caste_system_among_South_Asian_Muslims Buddhists also converted to Islam in large numbers, especially in east Bengal IIRC.