if you’re just planning to aggregate the data in the end, you should download the aggregated data instead of downloading observation-level data. see: https://forum.inaturalist.org/t/data-extraction-from-observation-fields/34872/6.
for example, this will give you daily observation counts for one of your projects: https://api.inaturalist.org/v1/observations/histogram?project_id=a-borzsony-elovilaga&interval=day&d1=2020-01-01.
you can work with that raw data using your own favorite tools or scripting languages. or there are several tools created by iNaturalist and by third parties that will get that data for you and visualize it in different ways (see the first link above). here’s one i created just yesterday: https://jumear.github.io/stirfry/iNat_calendar_heatmap?project_id=a-borzsony-elovilaga&interval=day&d1=2020-01-01.
If you really want to get a random sample of observations, it’s possible to do that via the API. you can simply specify the parameter order_by=random when retrieving data. If you’re interested in doing that, I can describe in more detail how to do that.
depending on what you’re trying to achieve, there are ways to get more observations, such as via GBIF, the AWS Open Dataset, etc…