1. You've entered comma or dot by mistake, depend on your settings one or the other is wrong in 1 or more equipement.
2. belongs to point 1 I guess because there's not a big difference between 208 kg or 209 kg
3. That depends on your settings of the plugin is individual (tyres, position etc.). Everything depends as well on your smoothing settings in ST. You shouldn't compare different calculation like ST and Strava it's anyhow more or less
just a calculated estimation. Compare this numbers only within the same application. Best would be to buy a power meter

to get real numbers.
I might buy a pricy here soon:
https://www.indiegogo.com/projects/team ... -bicycle#/