Question 1 - do tricos hatch then fall shortly after or is what I witnessed today a hatch and a spinner fall from a previous hatch?
male duns emerge before female duns. In hot weather, the males may emerge during non-daylight hours, any time from late evening to early morning. During cooler weather, the male duns are more likely to emerge early in the morning. This is followed by emergence of the female duns, often from dawn to mid-morning, or if the temperature is extremely cool, it may be delayed a few hours.
In any event, getting to your question, Tricorythodes
duns molt to spinner stage after only several hours, so (at least) the females would be those that had emerged several hours earlier, often resulting in a spinner fall commencing while female dun emergence is still happening.
Having said that, there are no absolutes with regard to mayfly emergence behavior. So, exceptions to what would be considered customary emergence behavior do occur, likely the result of some condition(s) not favoring successful emergence, mating, and oviposition.