Here is a more detailed guide to help you upload and share your map with other people:
When you export your map you will notice that the map will list files is has exported from the map. For example [MapName].fhm, [Object].fho and so on...
Just make a list of those files and go into Local Disk (C:)\\FeralHeart\\Exports and find the files that were listed. Once you've done that, drag and drop those files onto your Desktop (Make sure you have made a folder on your desktop to place them in!)
Once you have done that, right click the folder and select 'Send to'\\'Compressed Zip Folder'. Then go to a file sharing site (Such as Mediafire) and upload that folder there. Once you have completed that task you can then share the link to anyone you please.
As for your other questions, as said above, the limit of people in one map at a time is 300. Glitches will not happen as long as all files on the receiver side are placed into their Exports folder. If there are issues with any objects in the map (example; some objects missing) then that can be fixed.
Usually the case is that custom objects (objects/meshes/particles that you downloaded into the game) aren't put into their own group, just saved into the default groups in the object maker. In that case, you just need to save the objects into their own group in object maker and export the map again then share those NEW filed in order for people to see it.
You can access your map files in Local Disk (C:)\\FeralHeart\\Exports. Or if you want to access the Height Map and Terrain Map, all you need to do is go to Local Disk (C:)\\FeralHeart\\Media\\Terrains.
Hope this cleared things up for you~ If any further assistance is needed, don't be afraid to ask!