Issues with high traffic and a lot of POI on the map

Good morning,
I'm a user of My Maps Location (I have used the Pro version and I have to renew it).
I have integrated the component in a web site of an onlus but I have some issues with it and I would like to know if it is possible to fix this bugs.
The onlus organize two big events, one for Easter and one for Christmas, during which people have to seek the locations on the map to know where to find the stands.
I noticed that the high traffic of users (10.000 or more) at the same time is not supported from the map: for example if a user search for an address the "nearest" POI on the map will be in a wrong position (another region of Italy).
I also have problems with the import of the locations that I have to record on the map: I can import only 200 addresses at a time because if I import all the 4000 addresses all together the program crashes.
Furthermore it will be useful if I could see all the locations on the map at the same time, and actually this is not possible.
Can you please give me an estimate of time and costs to do this kind of maintenance work?
Thank you in advance

Laura