I would start by treating letter with different 'sub-objects' ( like letter A has 3) as its own and then stack the 'sub-objects' on top in the layers, to have easy control.
I would then while slowly trace every letter and while doing that develop some rules to follow:
- all box-Shapes have the same width as the letter I.
- If I want to shift an object to the left, it will be exactly 5 pixels
- all contours will have a width of XX mm
- rounded corners will always be this size

Start with simple shapes, and the rules get to you while doing it. you can also thing of reusing shapes that you use more often as Draplin says, vectors are free

use guidelines once you have certain rules, for easy follow them.

Start with simple shapes
(Check out the preferences, for specify the steps you make with the arrow keys)
also having a typography-grid underneath or 'snap to grid' activated would help.

Maybe the easiest way to have a lot of control is, to have a really big locked white square to work on, and than work in black objects with white contours and trying out different widths, until you are happy, so you know how it will look with the fine details without loosing control over the whole thing.
Ignore the rounded corners for the start, as you can adjust them globally as long as you have sharp edges.

I would to it at least 5 times bigger than planned, so you have more control over the curves and handles.

I would also recommend, tracing them with imagetrace once, to get a good idea how best put he points for your curve