Roman3R :
Thanks for the reply m8, I think I have decided on getting a Powerline Adapter, but will I be able to connect to the _EXT router also with the adapter, or will I have to connect it to my main router?
You can connect the Extender with the powerline adapter, but since you have a N300 near your devices, what you can probably do is connect the first adapter to the main router, then connect the second one to the N300, and use the N300 as a Switch. This would allow you to use the N300's multiple ethernet ports to connect all your devices. You might need to configure some settings on the n300 to get this to work, or you might not.
The great thing about the powerline adapter is that if you decide on connecting all your devices with it, you won't even need the wifi extender anymore, which ought to help with lag and connection times.
Now that I've said all this, I'd like to add a little disclaimer:
Although I recently had a slightly similar situation to yours, I wouldn't call myself a networking Guru just yet. The only thing I'm not 100% sure about is being able to use the N300 as a switch (Though I honestly can't see why not). I would recommend doing a bit more research yourself to see if it is indeed the right solution for you; just because you get a powerline adapter doesn't necessarily mean all your problems will be solved.
Also, I've found that on my home network, (I have all my devices connected to my main router via wifi) I can have at most two bandwidth heavy applications or devices operating simultaneously without too much lag, but the third usually starts killing it. I have the best internet plan I can buy in my area (50MBps / 5MBps upload) too.
To get you started, here are some good links regarding pros/cons of routers, how to optimize your router, powerline adapter pros/cons, and other etc.
NCIX.com has a good video on all three networking types:
http://youtu.be/Sue1Zvmh8JA
LifeHacker also has a good series on routers and router optimization:
Router Hardware 101
Another Lifehacker post on the three network types:
Ditching slow Wireless Speeds
If all else fails, the powerline adapters are still excellent (relative to wireless) for gaming; I'm planning on buying some for my devices in the near future. But as I said, you might need to prioritize one device over the other.
I hope you've found this helpful. Good luck, and if you have any more questions I'll do my best to answer them!