1. Per user plan (cost $15 per user/month) does not allow you to create Desktop Flows, only cloud flows
You do not need this if you want both cloud and desktop.
2. Per user plan with attended RPA (cost $40 per User/month) allows you to create cloud flows and desktop flows, and run those desktop flows in attended mode.
So this is the one you need to build desktop flow, build cloud flows to schedule the desktop one, and to run it in attended mode.
You assign that license to you or other people who want to build cloud and desktop flows. You do not assign it to the GeneralAccoutning. That account is just a windows user where the flows will be ran.
3. Only if later you decide you want to run those flows in unattended mode - then you need to buy the Unattended RPA for 150$.
This addon license is not assignable to users but to the power automate environment.
So if you have 1 env and want to run 1 unattended bot at the same time - you need 1 addon.
If you want 2 unattended runs at the same time - you need 2 addons.
If you have 2 environments and want to run unattended runs in each - you need 2 addons, 1 for each environment.
But if attended runs are fine for you you, then you don't need it - license prom p2 is all you need then.
There are also alternative pay-per-use plans, but I do not use them so can't advise if they are any cheaper in your case, you would need to count how often and how many flows you would be running.
Please mark the answer as solution too, as now actually marked the one that is not correct and might confuse others