Well to be really sure you must get su up and running. I think having BusyBox will test whether you really "have root", or you can get an app like Root Checker (just search, pick the first result).
But otherwise that should really be about it, because the objective was a root shell (the environment that lets you run commands). You see, you were able to create a file in the system partition. That means read-write access to /system, which in turn means being able to modify anything in that partition. The Superuser app is merely a wrapper around the su binary, which forwards any request made to it.
But that also means the Java layer is dependent upon the su binary. Even if you have root via ADB, if su for some reason fails to run properly (it can happen, as it did for the stock binary on my W10), it's as good as no root and you're left to do everything manually (no nice root apps).
You have to keep in mind that one can't really "move" apps to the sd card by just moving the APK. This is because the data the app stores is still on the internal memory, in /data. Thankfully this is where apps like data2sd come in. However, I myself am rather new to Android though not to GNU/Linux (an OS using the Linux kernel for the desktop) and I have yet to do anything more than remove the bloat. I am slowly filling up the internal storage once more.
Building a ROM based on a popular custom distribution (CyanogenMod) should be a reasonable target, but it's not looking trivial at the moment because of the lack of dual-sim ROMs. All you can do is basically repack (which are the ROMs you see currently for the other Indian and Chinese phones) with themes and stuff. Do nudge this thread or PM me if you happen to chance upon a custom ROM for such dual-sim phones, or we may create a new thread which could serve as a placeholder for all things Symphony.
Don't mention it. We jump in to tinker with these phones, we potentially help a small minority out there who cannot afford or have no access to better phones. So far we can vouch for the Symphony Xplorer W10 and W25