The charts symbols are displayed at particular sizes on particular map types in the chart manual and Annex 4. However for electronic charts and visualisation in GIS sizing is very tied to the view level or magnification. It is also the case that the type of service that you serve out will allow you to see differnt features and label types.
A lot of work still needs to be done by ICAO and the community to decide for visualisation and electronic charts have the correct detail at the correct view magnifications and not hide or miss important details.
As mentioned during the webinars the size of your typography and your symbols will depend on the scale used for print. I would normally recommend that you lock the print scale in your map so you can use that to see if a symbol and label is readable.
Making test prints might be the only effective way to know if something is working and then you can measure on paper the size of items and usually before hand you would have determine what is the size that makes items readable. Once you have created your database of size vrs scale output then you will no longer need to figure things out by print as you would basically have a standard.
In the case of web maps then your size will depend on the scale you are viewing this will require you to create different symbology depending on how zoom in/zoom out you are including the conscious option to not show certain features at certain zooms because it is not readable or worth it anymore.