You should download more ram...nah, joke
1.If you have unlocked bootloader and root, you can do anything in android now.
2.Android is built differently than windows and the rule more ram=better. It just doesn't like to waste ram, so it uses it to something and it's still smooth most of the time(for me on slim cm10 it was 150-220 free, now on stock based rom it's 50-90 and it feels even smoother) If you want the games to run smoother you can flash a kernel with overclocking capabilities, but it shortens the lifespan of SoC, produces more heat and drains more battery, but if you are modifying your phone do you care about those things or performance?( I'm currently on 1.8ghz oc heheh)
But what you can do to free more ram are those things:
-uninstall apps you don't use
-use "greenify" to hibernate apps that always run in the background. Facebook in the background really slows down J
- STAY AWAY FROM TASK KILLERS
3.Cyanogenmod - custom rom for android phones based on aosp(stock android made by google). It's basically just stock android with additional functions.
4.Custom rom - it's simply a rom that isn't made by the manufacturer of the phone(it isn't stock), like cyanogenmod
5.System recovery - really it's just what it sounds like, although custom recovery is more common - clockworkmod or team win recovery project. They are essential if you want to flash a custom rom or install some mods or do other things such as formatting the system, wiping cache or simply making a backup of the system
6.It is possible to downgrade firmware - you just download the desired firmware and flash it
7.Probably no, but you don't really need to worry about this - J has two firmwares - 4.0.4 and 4.1.2. and it won't get any more official updates - you can flash them with flashtool without worrying about it and there is really no need to use 4.0.4
8.As i said before - use greenify to hibernate apps.