Ac55uhp is high power router. Usb 3.0.

Bit expensive than AC1200G+

Hi carz,

1) will a RT-N14UHP Wireless N300 router be of sufficient speed (802.11n : up to 300 Mbps) for my use ?   
For 50Mbps, I would suggest you to got for AC router, because even TM are giving AC model for new applicant.
This is because with the 5GHz, you can easily get 50Mbps on WiFi.

2) It should be sufficient to support as many users as I need without maxing out the bandwidth right , since the unifi is only 50 mbps ?
There is a limit on how many clients can connect to the router, the 50Mbps are shared among the clients. If someone is downloading and streaming, the clients will pull all or most of the bandwidth already.
For RT-N14UHP around 30~50 clients. The higher the hardware specification such as RAM and CPU, the more clients it can connect.

3)  One of the device connected to the wifi network is a smart TV streaming movies.  What setting should I make to ensure that it has priority for the bandwidth to ensure there is no buffering ?   How much bandwidth do I need to reserve for the TV?
You can try use QoS to set the priority for the connected clients.

4) What does "Guest Network : 2.4 GHz x 3" ?    Does it mean that it can only support 3 guests ?
Guest network mean you can turn on another SSID to allow your friends or family to connect to. The clients that is connected to Guest Network has their network access restricted(such as unable to log into router and unable to discover other clients in the network). 

Thank you

I just bought WD My Passport 1TB drive and connect to the USB port of my ASUS RT-N66U (firmware version 3.0.0.4.380_7378). I formatted the drive as NTFS as I want to download files larger than 4GB limit. The problem is It always show "Unmounted" status no matter I switch to another USB port. May I know how to solve this problem?