1) Establishing formats in templates is very easy to do in Prime. You can change your default formats for text, math, document layout, etc, and save that as a template file. Then you can tell Prime to open that template as the new default every time you open Mathcad Prime
How does this differ from Mathcad 15? I create and use my own templates, including a modified default, and have done so since at least M11. From your comments, it would seem that I have the ability to actively manage which template is the default, but given that the default worksheet is likely to remain as such for long periods time, I'm not sure that it adds greatly to the capability.
3) Both legacy Mathcad and Mathcad Prime have excellent capabilities in unit handling and unit conversion. However, one of the major advantages of Mathcad Prime over legacy Mathcad is its ability to label variables, constants, functions, units, etc. This makes defining new units extremely easy. In Mathcad 15 and earlier, you created new units as simple variables. In Prime, you can actually designate a newly defined unit with a unit label, which will cause that unit to appear with different formatting (default is bold, dark blue letters) to alert users and viewers to the fact that it is, in fact a unit.
How does this differ from the use of Math Styles in "legacy" Mathcad? Again, I've used those for years to distinguish between scalars, strings, arrays, function arguments, local variables and units. By renaming the styles to have a unique first character, they're reasonably easy to apply with the key sequence Alt-0,Enter,<style character>,Enter, as well as from the drop down menu. Styles could definitely have been better supported from a user perspective, but they were always there.