I'm a owner and SharePoint developer of website service based on AVL and Orders optimization. Optimization of realtime Orders ( Call-based transportation service) with realtime random locations of Cars (based on AVL technology) builded on proximity analysis, which you need for your app.
In my case both Resources and Tasks dynamically moved, in your case, as I undersdood Technicians (resources) almost stable (address based SP List), but Orders need to be geolocated/reverse geolocated in process of order creation.
I'll be glad to complete your task. Its someting interesting for me, in GIS more than 15 years, more than 5 years in SharePoint.
Skils: GIS, SQL, MS SQL Spatial, SharePoint, WebHandlers, SP Event Handlers, Google API, HERE API.
There are some questions I can prepare about limitations, capacity and workload of your app. If you interested.