Which GIS to choose?

Question

OpenStreetMap

Hello!
Guys, can you tell me, please, in which direction to "dig"? We need a tool that implements the following tasks:
1. Geocoding. We currently have about 500,000 objects for which we need to get coordinates. There will be more to come. This question is very important, because all other information depends on how correctly we tied to the coordinates. Possibly OGC? You may need an algorithm for recalculating to the selected coordinate system from others. We must choose the one that is the most correct for our tasks and features.
2. Connections. There is a lot of information that we need to link to each other somehow. For example, the administrative division. There are object coordinates, there are district boundaries. It is necessary to automatically or upon request put down the administrative region for each object. As I understand it, this is Overlay and Proximity Analysis.
3. Mapping and data editing. So that you can draw your own maps, add, change layers. I do not think that multi-user and access to limited information will be required, but if there is such an opportunity, then it will be good. Add, modify, and delete points, lines, and polygons, edit feature attributes, perform multi-user editing, and follow the rules for behavior of feature classes.
4. Display on the client side. The use will be internal.
5. Data storage. Or access through the API of third-party services, but "warehousing" on our server.
6. REST. Upon request for object coordinates, return all links with other objects on the map, layers, etc. Ideally, I would like to set conditions for the required search for objects, layers (all layers that the query coordinate "crosses"), etc. For example, define that you want to display all POIs within a radius of 3 km. Those. we know what layers we have and set the conditions for displaying information to the query conditions

Answer 1

ESRI ArcGIS Server is the best solution available today, but is prohibitively expensive.
Some of your tasks can be solved using QGis or NEXTGIS + PostGreSQL + PostGIS + Data (eg OpenStreetMap) + Coding.