I guess a sect (सम्प्रदाय ) is one that only subscribes to a subset of Hindu beliefs and/or worships only a subset of Hindu gods. Is there anything in scriptures about this? What is the etymology of the word SampradAye (सम्प्रदाय)?
Yes there is. Srimad Bhagavatam explains the reason for differences between sects.
Explanation of different interpretations
Just as one object with various attributes is seen differently through the different senses (say, a flower fragrant to the nose, soft to the touch, and beautiful to the eye), - even so that one Bhagavan is viewed and interpreted differently by different philosophies and scriptural writings in the light of their particular traditions. (He is one and the same, but each religion or philosophy seeks to interpret Him in consonance with its own tradition and concepts.)
Srimad Bhagavata Purana, translated by Swami Tapasyananda, III.32.33
Etymology: sampradAya = sam + pra + dAya "a bestower, a presenter".
- sam: "(together) with"
- pra: "forth"
- dAya: derived from root dA "to give, to present, to offer" dAya = absolutive II
All lexical meanings are from