Dynamic Components are parametric. The ability to create a DC is a pro feature. But anyone can use a finished DC. Probably best to view the YouTube videos and download some DCs through the Components dialog. DCs have a little green symbol in the lower right corner.
There once was a commercial plugin called Driving Dimensions which dynamically changing dimensions. But apparently it didn’t generate enough intere$t.
Regarding the holes you are encountering while modeling, you are getting them because the small size of your models. If any tool operation ends up creating new geometry with any edge around a mm or less, holes can result. This is bumping into a limitation of OpenGL. There are two way to avoid this holiness.
Temporarily Scale up your model 10-1000x, do your modeling then Scale down when done. The other method first needs you to make your tiny part a Component. As all copies of the same component will change with each editing you can exploit this property. Make a copy of your tiny component part and paste it off to the side. Select the component copy and Scale up the copy. Then double-click the enlarged copy to edit that now oversized geometry. The changes you make will be seen in the original component.
Delete the large component copy when done or just keep it around to be able to be able to view that part with greater ease if the original component is a bit buried among other part in the main modeling area.