I worry bout the complexity and that's why I try to get helps from available map frameworks (like urs)

Anyway, have already marked ur asset and will purchase it once the $ is right for my budget

To make the multiplayer you need to use Photon, Smartfox or any other multiplayer framework.
You can try to implement the server side by himself.
But do it right and safely is a pretty difficult.
So I recommend you to use some framework.

After that I found your asset and wonder how come the approach so different as ppl mentioned
Display custom map - KML/KMZ
Show custom market - using fusion table

My worry is purchase the wrong product

You can create markers using the inspector or using Online Maps API.

2. No, Online Maps does not use Fushion.

3. By default markers are not clickable.

4. Google API Key is not used in requests for downloading tiles. The key is only used in requests to Google Maps Webservices (Places, Geocoding, Directions, etc.).

I studied some google articles,

- How can i show my *.KML map (monster map), also they mentioned the best would display custom market through Google Fushion Table.
- Does the plugin using Fushion? if Yes, HOW to do the magic in this asset?
- How can i make the marker not click-able (if one player clicked on it)

also, it doesn't show a place for us to put in our API key

1. Yes, you can create your own map with monsters.

2. Yes, you can have the user generated content.
But all client-server interaction you need to implement.

3. http://infinity-code.com/atlas/online-maps/index.html

I am very interested in
https://www.assetstore.unity3d.com/en/#!/content/13261

Sorry if i posted some silly questions below
- Does it support custom map? E.g. i can create my own map and posted 100 monsters in diff location in my map
- if YES, possible to have user generated content? e.g. game player can upload their created monster and the other player can whack the monster created by other player
- Any tutorials or guides on the items i mentioned above?

Hope to hear from you guys more