Did some quick test to replicate your work environment. I have done the following:-
- Loaded around 10 files in Photoshop- a combination of complex layered PSD files (with text and layer effects) as well as a few RAW photos
- Opened 20 tabs on Safari (a combination of pages with complex Javascript, YouTube (with videos playing), Flickr, 500px, news sites, etc)
- My productivity software (Outlook, Microsoft Teams, OneDrive, Slack) was opened in the background
- Tidal playing in the background
Observations:-
1. Loading in Photoshop (average file size between 80-100MB for the layered files and 50MB for the RAW photos) was extremely fast
2. Everything that I was playing in the background (music from Tidal, YouTube videos on the tabs) was still playing without any lag or pauses
3. CPU load was at 20% (Idle standing at 79.82%). Biggest CPU hogger was Photoshop which took up 25.8% of the CPU. Not much CPU pressure here.

4. Swap file was at 6.44GB while 12.37GB of RAM was used up. Not much memory pressure here.

Overall, 16GB would be more than comfortable for what you need. Do bear in mind that Photoshop hasn't been optimized for the M1 yet so it is still running under emulation mode with Rosetta 2. Even then, it still performs better than my current 2018 Intel MacBook Pro! With an Apple Silicon version coming in Q1 2021, expect more efficient RAM and CPU utilisation.
I usually do not run Windows under Parallels on the Mac. Actually, I've haven't got much software that I can't do natively on MacOS. Also, there is no Parallels that work with M1 yet except for the Technical Review that they have right now. Even then, the Technical Review only emulates an ARM machine and you need to install the ARM version of Windows (also a preview). From YouTube creators initial trial, it is not looking like a workable solution yet as it is pretty buggy and slow. And Microsoft's x64 emulator on the ARM version of Windows is also pretty slow and doesn't work with all software yet.
Every time I load it up it will crash and not load. Lightroom and Premiere Pro works fine.