No, if your web server has access to your OpenSimulator database.
Yes, it works too. Use OpenSim database credentials when requested for Robust credentials.
This is an OpenSimulator design limitation. Regions rely on cached data to display avatar information, and once fetched, these are never updated. As a result, if an avatar's name (or grid URI btw) is changed, the change would not be reflected on regions already visited by this avatar (which will still show the old name), but new visited regions would display the new name. This could be somewhat handled for a small standalone grid, but never in hypergrid context. There is no process to force a foreign grid to update its cache, and probably never will.
No, you don't need to and you shouldn't. The /helpers/ is virtual, it is served as any other page of your website. Like there the /about/ URL website doesn't match a /about/ folder your webste directory. Even if there is a helpers/ directory in w4os plugin, it has the same name for convenience, but he could have been named anything. It's content is not accessed directly, it is used by the plugin to generate the answers. On the opposite, if there was an actual helpers/ folder in your website root, it would interfer with w4os.
Yes and No. It can improve a lot the images delivery speed, but you won't benefit of the cache expiry, which would eventually correct any wrong or corrupted image.
Divi Theme support is fixed in versions 2.4.5 and above.
Don't even finish that sentence. Versions of OpenSimulator older than 0.9 are definitely not supported anymore. You might be lucky and it might work, or not. In either case, idk&idc.