Many devices are limited in storage capacity and there is no guarantee that the build system will detect when you have added too many packages to fit into the device storage space, which may render the device unbootable if installed. If in doubt, do not go overboard. Use what you had installed on the device last as a guide or create a minimal image first, install it to the device and test what you would like to add first.
Image builder is using strong compression to reduce size. How well something is compressed depends from how it was made.
The only way to compare is to make an image with image builder with default packages, and then an image with default + your additional packages.
Then you know how much space the new packages you added will need.
In general, it's better to use Image Builder if you can do so, you use a lot less space if you install many packages