Yes, it comes with a USB charging cable that needs to be connected to the computer to charge.
Scope of delivery:
vívosmart 4 fitness tracker
USB charging/sync cable
Quick start guide
https://buy.garmin.com/de-CH/CH/p/pn/010-01995-01#box
Manual page 10-11
http://static.garmin.com/pumac/vivosmart_4_OM_DE.pdf
Actually I do not know. It shows always the AM / PM format. However, in settings there’s a section time and date. If it is not there, then the format is fixed.
Yep, alarms can be created via the Connect app. I don't use this feature, but I entered one once and forgot about it... The permanent vibration actually wakes you up quite well and is not as easy to set as a smart alarm.
Both smartwatches can be seen independently of each other in the Garmin Connect app. However, there is no "interaction" between the two models. The Garmin Fit Junior 2 also has a special / different software than the Vivosmart. :-)