Can I start processes per modelname via rest-ws api only if I dont use empty space in the name?
For example: http://10.10.1.247:8080/rest-ws/service/bpm/process/?projectpath=my models/model v.2.3 dont work.
You have to encode the url correctly and than it will work. Please take a look at: https://en.wikipedia.org/wiki/Percent-encoding
But I recommend that you do not use special characters in model names.
As described in documentation:
"The technical name must start with a letter and may only contain letters, digits and underscores."
So, the approach that is described by Christian is a workaround, for a feature that is not supported.
The correct approach is to use technical names that are supported (in particular since the functionality for such workarounds may change at any time and without notice).