For the L7 router, the bandwidth limiting feature would be called 'QoS engine'. It would be located under ADVANCED > QOS Engine.

Screen shot of the QoS engine page: http://screenshots.portforward.com/routers.../QoS_Engine.htm

Better go for those router that can do ip based traffic limit

TP-Link-> IPQoS feature enable router
ASUS->Asus WRT loaded routers

Wat is your budget in mind?

I assume yours is UniFi service.

TP-Link (make sure there is Unifi Support Logo or else you have to update firmware manually for it to support UniFi)
1043ND
WDR3600
WDR4300

Asus
RT-N12(Be careful with HW revision C1, you have to update firmware if you get this hw revision for it to support UniFi. D1 is support out of the box)
RT-N12HP
RT-N16U

Dual band refers to the wireless frequencies that the router is able to support, namely 2.4GHz and 5GHz.

A quick and brief description about the two can be found here: http://www.tp-link.com/EN/article/?faqid=499

FYI, in order to use the 5GHz band, you will have to make sure that your wireless device/adapter/laptop is able to support the 5GHz band.

Google is your friend
http://www.theguardian.com/technology/askj...wi-fi-zip-drove

Get ASUS, they are pricy, but much more stable compared to TP-Link.
TP-Link provides crappy & rarely updated firmware.

How do I know? I've own several TP-Link & ASUS routers.
Tested all of them, ASUS is still the best.

My list of routers:
TP-Link:
TL-WR1043ND
TL-WDR4300

ASUS:
RT-N16
RT-AC68U

That depends on your budget.
Personally, I'd recommend the RT-AC68U because of it's speed, reliability & wireless coverage.

But if budget is limited, RT-N16 then. Still better than any TP-Link routers I've ever used.

Cheapest AC68U would be RM680.

With your budget, here's what you can get:

Routers with internal antennas:
ASUS RT-N13U - RM159
ASUS RT-N14U - RM199
ASUS RT-N15U - RM190
ASUS RT-N53 - RM248

Routers with external antennas:
ASUS RT-N10U - RM139
ASUS RT-N12 - RM117
ASUS RT-N12HP - RM179

Note:
I've never used any of these routers I've listed above, thus I do not know if they have the bandwidth limiting capability. You'll have to google them out yourself. I've only used RT-N16 & RT-AC68U.

You can't.
You'll have to try it for yourself.

There's a reason why external antennas is always better than internal antennas.
Routers with external antennas are mostly upgradeable. You can change the antenna into a better one to increase it's range.
Routers with internal antennas however are not upgradeable.

I've always stayed away from routers with internal antennas.
Yes, been using the download feature since the first day I used RT-N16. It's also available in RT-AC68U.
The router will download torrents & save it into any USB storage that you connect to the router.
This way, you can use the router to download torrents & not having to turn on your PC / laptop to save electricity.

Just remember this, once you bought the router, remember to change the admin password so your cousin wouldn't be able to change anything inside the router.

Consider adding a few extra bucks for the RT-N16.
The extra USB port can be used to connect to a USB printer & change it into a network printer.
With that, you can print from Smart Phone/PC/Laptop/WiFi Capable Cameras within the network.

1 port for USB storage, 1 port for USB printer.

RT-N16 vs RT-N14U
USB: 2 ports vs 1 port
Ethernet: Gigabit (1000Mb/s) Lan vs 100Mb/s Lan
CPU: Broadcom vs MediaTek
Flash: 32MB vs 16MB
RAM: 128MB vs 64MB
Antennas: Upgradeable External vs Non-Upgradeable Internal

3rd Party Firmware Support:
RT-N16: OpenWrt, DD-WRT, Tomato & Asuswrt-Merlin.
RT-N14U: None.

The cheapest would be RM329.

Used RT-N16 before as DualWAN Router , for 2x1Mbps Streamyx, QOS and bandwidth monitoring.

Asus RT-N16 is really a good hardware and platform for customize.
Recommend for advance super, but beginner may choose other to use stock rom or other model.

You may want look at this
http://event.asus.com/2012/nw/dummy_ui/en/