Improving my Network. Need opinions

Currently I live in an apartment at my college with 1 roommate. I'm the main internet user (I'm sure I'm 99% of the 150GB of data used this month alone). She mostly uses the internet to check facebook on her MacBook and iPhone and listen to music. Her boyfriend is no different in his use when over or any friends of ours. Me however, I'm running a tablet with a weak a/b/g/n card that seems to never get a higher theoretical data rate of 65mbps and more so averages 6.5mbps. I have a Sager laptop with an Intel 6300 and a old Dell laptop that I keep wired up as a Media Server. I have an Xbox running a wireless a/b/g adapter and a Windows Phone.

I was content with my network when we were paying for 25/5 and I would often see 29/6 on my 5GHz band in my room. But Comcast offered us a new deal that ended up cheaper in the long run, doubled our internet, and added cable which my roommate wanted so I jumped on that fast (only downside is there is one cable jack in the apartment so I will be running a splitter from it now). And of course, my download speeds in my room didn't actually increase.

I often keep my Sager laptop setup in a desk environment hooked up to a keyboard, mouse, and monitor. My tablet has become my on the go computer. So I'd prefer to have my Xbox and Sager wired than wireless for the better latency and speeds. And now that I can get much higher speeds wired, I want wired. On my Dell, I've turned off the wireless radio and use it wired only. I'm getting speeds on average of 57/12 on it. My Sager still averages about 28/12 now on the 5GHz. The 2.4GHz I usually never see more than 10/10. My room is about 25ft from the router with one wall between it (see attached pics).

Currently my roommate only uses the 2.4GHz band. The only other items on that channel is my tablet (I try to use the 5GHz channel, but my tablet almost always drops it from my room) and my phone but I often turn off the wireless radio because the 3G seems to have lower latency half the time than the wifi on it. It is worth mentioning that from where I sit typing right now, I'm picking up about 30 other wireless networks. About 99% of them are 2.4GHz and there seems to be an even distribution of networks running on channels 1, 6, and 11 so I have no clue which channel I should use (right now on 11).

I'm the only one on my 5GHz band, there is maybe 1 or 2 other routers running that band in the area but they are very distant. I use the band for my Sager, Xbox, and when possible Tablet.

I own a Netgear WNDR3400 which I really regret right now because it isn't N900 (for the Intel 6300) and it isn't gigabit LAN (I transfer data between my Sager, Dell, and Tablet all the time). In a few days when my supplies arrive in the mail. I will be moving my router and modem (see pic1 and pic2). The modem is currently on a 20ft or so coaxial cable which I will now be running over our sliding balcony door closer to our bedrooms, I'm then moving the router using a 50ft cat6 cable into my room where I will be wiring up my Dell, Sager, and Xbox (and Tablet as necessary if I ever purchase an Ethernet adapter).

I'm a little worried that with the router in my room, the 2.4GHz band that my roommate uses may weaken since there will be more walls in the way. I've been contemplating buying a used router on eBay such as a Netgear WNDR3700 so that I can get gigabit LAN speeds for my devices. I really want the Asus RT-AC68U but I don't have over $200 to spend on a router I can't fully take advantage of yet. I'm looking to possibly spend no more than $30 if I do buy a gigabit LAN router.

If I do buy a router, I was planning on selling my current one, however, it has the ability to be a repeater. I have no clue though how repeaters work other than that they take the signal in and amplify it without changing any other aspects of the signal. I don't know if boosting the signal though has any affects on the actual throughput or not as well as if a repeater in a 2 person small apartment is problematic or not. In a perfect world I'd be able to use the gigabit router as the repeater (so that I don't have to run long wires anywhere) and wire up my devices, but I know I'd still not have as low of a latency as straight connected.

What are your recommendations for improving my network (especially the congested 2.4GHz band)? Is buying a gigabit LAN router worth it at all? Is using a repeater worth it or going to help? Below, the 1st pic is my current setup and speeds I get. Pic2 is what I plan on setting up in a week when I have the time finally so that I can get full speeds on my Sager and Xbox as well as finally have fast throughput and no longer need to play piggy back with an external HDD to transfer data between my Dell and Sager.



Edit: I think it is worth noting that sometimes in my room, my 5GHz band seems to just stop working right once in a while and I have to switch over to 2.4GHz for my Sager. Not sure if that is a router issue (sometimes turning it off then on fixes it).