I only used the BT for setting it up the first time as i found it more convenient. It can be done manually though. The app itself is pretty crappy and not useful for me so I just uninstalled it. If the watch is not paired with the app it won't use Bluetooth so it won't be draining battery. Even if you let the app installed and notifications active I don't think it drains that much as the watch battery is stated to last around 2 years this way. I don't use BT and don't use backlight that much so I only have swapped battery once in 4+ years.
Alarm is easy to setup but is old school watch which means that if you want an alarm at, let's say 6:30 and said alarm is currently set at 6:00 you'll need to select the minutes and then press 30 times. It can be done faster via the app but unless you are constantly changing your alarms around I don't think this might be a concern.