Which routing service are you using? Only Monav (offline routing) delivers instructions that can be used for voice guidance. The online services (OpenRouteService and Yours) only have textual instructions.
Start mapping them That's the great thing about OpenStreetMap, you can extend it easily.
Service providers .... Technically that's easy .... Please note however, that using them will likely violate the terms of use of the respective provider! ...
Way points can be removed from the routing dialog (the 'clear' button inside the input field).
Can you describe what you are doing in more detail when it zooms out completely?
Unfortunately some of the elements used in the overlays (info boxes) handle too many mouse actions by themselves. Especially for labels that's annoying and the reason why e.g. the speed info can only be moved when grabbing it towards the borders.
Monav .... That's true for offline search. A case-independent search would be too slow on mobile devices when using sqlite. Online search services should be able to handle it though.
Monav slowdown .... No, that sounds strange. Does that happen in a reproducible way?