Welcome to the Group, Winifried.
I am sorry to report that there is no data on the One-Name Study files for WELLERs in Dover or of glass-makers (yet!). Perhaps surprising when there is data for over 80 Kent parishes in a total of over 400 in England, supplied by 300 contacts. Do you have a date and name for the mayor of Dover? Does any other Group member know about glass-makers?
Regarding your request for information about Jewish WELLERs from continental Europe, I would think there is a better chance of help from American descendants. I am not aware that any such WELLERs settled in England (whereas my own maternal line was of German Jewish origin.) Others have researched American families with our surname, so I have cocentrated on the UK, which in effect means either Kent/Sussex/Surrey or Oxford/Buckinghamshire prior to about 1800. You might consider posting a message on Genforum's WELLER forum as it has many American subscribers.
I am so sorry I cannot be more help at this stage.
Richard.