Yes! (But please be careful.)
We fully appreciate that there is a need to support large research projects. I've been routinely using a project with 10k photos, but we have not run tests with up to 30k photos yet, so please bear with us in case there are issues, because this is new territory for us as well. My main concern with larger projects is simply that some actions may require optimizations at the database level that we're simply not aware of at the moment (because they're fast enough with smaller data sets). If you run into any issues, please do let us know and we'll do our best to address them.
Having Tropy access the photos directly from Apple Photos is something that we want to support (so that you don't have to duplicate all the photos) but it's not straightforward because Apple Photos does not invite this kind of interoperability. Currently, I think the best way to import the photos directly (i.e., without copying them first) is via Tropy's import dialog (the plus button) and selecting the 'Media' panel which gives you access to the photos. However, I have not looked at how you would access photos which Apple stores on the cloud. Please stay tuned as we work out the details for this kind of workflow!