> Is it typical for candidates to have their own platforms put forth outside of the incumbent party platforms by this point?
Most of the top tier (by current polling) 2020 candidates don't have much beside donations and merchandising on their website yet; Harris has some things that are at about the level of a stump speech and Warren has actual issue pages.
Those currently in Congress (e.g., Sanders, Harris, Warren, Gillibrand, Klobuchar) can (and do) signal platform positions concretely through sponsored legislation, even they don't have issues pages on their website.