F. Weber (Berlin) 1860-1929. This was the manufacturer. The other name on the fallboard was most likely the outlet dealer who sold the instruments for the maker. Lexow was a common action maker of that period.
This is a cottage upright-85 key, possibly straight strung, but I have also come across some of the German cottage uprights that were over strung.
For dating the serial number, most likely on the back of one of the action rails there is a signature and date of when the action/keyboard was installed. This is one of the last jobs completed in a factory setting so that date will get you close to the completion date of build. When you have the instrument tuned by as technician he/she might be able to find something to help there by removing the action.
There could also be writings on the key bed underneath the key blocks.
The instrument you have looks to be from the 1880’s-1910 era; that is when those types of legs were popular.
It appears that this one was painted at some point; but you are lucky as it also appears that the white paint was over top of the old varnish or shellac finish, so the paint is just sitting on top by means of mechanical bond, and is easily stripped away. If the original finish had been stripped away prior to painting the paint would never come out of the grain lines.
Unfortunately at the same time the chemical stripper will dissolve the original finish as can be seen on the cabinet with exception of the legs which have not been stripped yet.
Most of these Victorian pieces were in black walnut or some other dark brown tint as that was the popular colouring in those days.
Topic: Question about my F. Weber Berlin