Few things
1 - Do not make a unique SSID for each AP, that is going in the wrong direction 100% and does not allow roaming to work at all.
2 - Do not use NAT mode, this does not allow for proper roaming, you need to use bridge-mode and choose a specific VLAN for the single SSID
Clients will roam because the clients decide they want to, and using PSK it should be fast enough nobody will ever notice. NAT mode is desinged for single-AP coffee shop setups, each time you move from one AP to the other, you break all TCP sessions, so anything like wifi-calling etc., will hard drop each time.
Also I would make the SSID 5GHz only, and have another SSID that is 2.4GHz (support can enable the option for you to toggle 2.4 only mode if you ask them). This will ensure that dual-band isn't giving clients any grief. Also turn off load-balancing setting.
Make sure your TX power levels are not all over the place. I would recommend changing the minimum data rate to 6Mbps as well for management frames since you only have a few AP's, making it higher won't make any difference and might hurt clients that are flaky.
You will see client disconnects often, its normal. They go to sleep, or simple turn off, roam, go out of range etc.
Channel width I would personally take a look at. Check the spectrum. Is there a ton of other networks? If so, you might want to look at only using 40MHz or 20MHz. 80MHz is rare to get away with in business environments.
For the windows machines, make sure their drivers are updated for the wireless card (assuming Intel). 90% of the time its a driver issue. Android and Apple not much you can do about, they are usually rock solid anyhow.
