Help improving my wireless Network

I'm using my ISP provided router a Sagecom 3965 and it isn't able to provide me with enough wireless range to get wifi everywhere in my house. I decided to extend my network by using a power line adapter to my old Linksys E3000 router. I live in a 3 floor house  Top floor, middle and basement the main router is on the top floor in my bedroom and the bridge is basically in the room directly bellow me.  adapter i used if that info is relevant  

That's my basic setup, now the problem i'm running into is the bridge is more for my sister's computer and laptop so they can get on the internet but the connection is very spotty and random. Some days it runs great some days its total crap and unreliable. I have a few questions about the internal setup that i'm not sure about and hopefully you fine folks can help me with

1) Should both my router and bridge needs to be on the same channels ? Any free tools out there other then the Wifi analyzer app to help determine which is the best channels to connect too

2) My ISP provided router has a Web based control panel controlled by them It doesn't allow me to disable Mixed modes on 2.4ghz its on G/N and 5ghz A/N from some of the reading i did i should have it all on N ( To my knowledge i do not have any A/B/G devices any more so i don't think this will be a problem) The Linksys does allow me to do this.

3) Should i be managing 2.4 and 5ghz as seperate Networks ? The main router manages them as one by default but separating into 2 is a option. I have no idea if a device is connecting 2.4 or 5ghz, My Wifi analyzer app on Android is the only thing i have that can differentiate. Example i'm guessing I know 5GHZ has weaker signal and my Xbone gets like 60% signal strength even though the bridge is up the stairs and around the corner from it but still gets a 40/24 mbps speed rating so i'm assuming its on 5GHZ i know its capable of using it

4) Could it just be my E3000's firmware is just garbage? it's on a 2010 build apparently linksys made a update earlier this year but I've not seen anything positive about stock firmwares. I've heard that DD-WRT or Tomato do Wonders! on older Linksys routers but i'm kinda afraid of bricking the router 

This is the wiki for my router but i'm confused/nervous about what i need to flash because of this message DON'T BRICK YOUR ROUTER! AFTER FLASHING WITH THE TRAILED BUILD, IF YOU THEN FLASH A BUILD THAT DOESN'T HAVE e2k-e3k in the NAME OF THE BUILD YOU ARE FLASHING YOU *WILL* BRICK YOUR e3000 ROUTER. ALSO reference this post regarding the newer NV60K.BINS FOR ALL E~ Series linksys

Maybe i'm just bad at navigating around the dd wrt site but i cant find where the E3000 builds are or what would be the best to upgrade too? Is the Trail build fine to stay at ? or if this will even improve my situation. I'll keep searching their forums.

Any advice or guidance would be greatly appreciated i'm kind of at my at the end of my own knowledge regarding networking and would really like to resolve this problem. Having my sister stop nagging me about the wifi would be lovely too she thinks this stuff is all just magic and doesn't care what i have to do to fix it Q.Q lol Sorry for the massive post <3

Also i'm not opposed to replacing my Main router for something with better signal strength and range if that will help. I'm not really digging this router i had a NetGear N600 prior to this that had better wifi range but still controlled by Optimum. Also not a big fan that they use my router to Broadcast a Free public wifi signal for their public wifi service 

1. They shouldn't be on the same channel, because then you will get some nasty interference and your devices won't know which piece of hardware they are talking to. I have an old E2000 as my secondary router with my ISP provided router as my primary one. I tried the same channel and it broke everything.


2. I have mine on N only as I don't have anymore G devices that get much use anymore. N only should also allow you to have higher speeds because the router doesn't have to maintain any compatibility with older devices.


3. If you can have simultaneous 2.4 GHz and 5 GHz networks, then do it. Most newer devices can run on 5 GHz freeing up traffic on 2.4. Even though 5 has a  shorter range due to it's higher frequency, it's higher speed is well worth it (unless you have brick walls). I used the free version of inSSIDer to check for interference. Depending on your neighborhood, one floor may have different levels of interference. I also live in a 3 level house, and I live on a hill. My top level has the worst interference with neighboring networks so picking a channel was a bit more difficult.


4. Before I got got a new router from my ISP, I used a WRT54RG with DD-WRT as an extra AP... way better than the stock firmware. As long as you follow the instructions to the letter, you should be fine.


I hope this can be of some use. It's funny because we have similar setup situations.