Pocket File Manager works just fine on 8.0, and has full access to the SD card there too. The 8.1 version could add more capabilities, but you don't strictly need it.
Camera quality is one of those you-get-what-you-pay-for situations. You bought a budget phone, with relatively low specs aside from its screen size. What did you expect? It'll give better camera performance than almost any other phone in the same price range, but no, it's not going to match a iPhone 5S or Lumia 1020 that costs 4x as much.
Not sure what you mean by "hide my application"; can you be more specific? I've used Android but not extensively.
The third-most popular platform is going to be the third to get apps, or app updates. In my experiences the first-party stuff works extremely well and the stuff from close partners is close, but third-party is a crapshoot. You could try unofficial clients, if you want; it's not that uncommon for them to be better than the official ones.
How much easier ringtone management do you want?!? It's the top item in Settings, and you can add custom ringtones and message alerts to any contact anywhere you can tap their name (People hub, Phone hub, Messaging hub, etc.). Creating ringtones from media files isn't easy with built-in tools but there are plenty of apps which can do it.
Call recording requires hooks at a level of the OS that could also be easily abused by malware. Microsoft could make a special API for that feature, but they haven't done so yet. If this is a vital feature for you, you should have researched what phones support this feature before buying... Most people never need it.
Dual-SIM is supported in the latest WP version, which your phone is upgradable to (which, I should point out, Android phones often aren't...). However, your actual phone doesn't have dual-SIM. If you wanted dual-SIM, why didn't you buy a dual-SIM phone, like the 630?
USB tethering is possible on some phones - for example, I can do it on my Ativ S - but it's unofficial. Is there some reason the official WiFi tethering doesn't work for you? You can still plug the phone into USB to keep it charged while you do that...
Win8/Windows RT projects:
List of desktop apps for hacked RT devices
Native Access WebServer and Libraries
WP8 Interop Unlocks
Storage Cleanup tool
XapHandler, Root Webserver, OEM Marketplace XAPs, Bookmarklets collection (Find On Page), Interop-unlock hacks.
Do not private message me with questions that should have been posted on the forum!
Not only are you wasting your time - I'm not going to bother writing an answer to such a question for only one person - but I will probably block you from PMing me in the future as well.