Install zh googlemap

Hi.
As for KML files - I think you can't do it. not only in my extension. I mean you need some managing KML's by zoom, ie on one zoom (city) you can see only cities kml's, on click - change zoom, and hide cities zoom and show the districs kml files. Like this.
But I don't support managing by zoom yet.

As for your data from your tables. You can simple create php file which connect to database and create some content (from database and so on).
And you can simple use Addition HTML field to call iframe to this file and pass some parameters, or you can use JQuery ajax requests to this file

Can you do it ( managing KML's by zoom) and connect it to data base
As paid project ??

Hi. As for connect to database - I wrote you. You can use your php file, some basic knowledge to create it, and connect and get your data from your database, after that format it. And display it by iframe call in Addition HTML field of placemark.

As for managing KML's by zoom - you shoud know, that you have limits for KML total size, which can be displayed by Google Maps JS API (check its docs).
And for managing - probably, I'll try to do it on next week.