I have a Dell Inspiron 5521 Laptop having 4 GB RAM. I am planning to add additional 8GB RAM.

So, the Total RAM would be 4+8= 12 GB.

I found the following information in Dell Specifications User Guide:

Memory

Connectors:

Inspiron 5521 Two internally-accessible DDR3 SODIMM connectors

Inspiron 5537 Two internally-accessible DDR3L SODIMM connectors

Capacity Up to 16 GB

Type:

Inspiron 5521 Dual channel DDR3

Inspiron 5537 Dual channel DDR3L

Speed Up to 1600 MHz

Configurations supported 2 GB, 4 GB, 6 GB, 8 GB, and 16 GB

I found the following Memory Module information by running Command on my Laptop: 

Total Width: 64 bits

Data Width: 64 bits

Size: 4096 MB

Form Factor: SODIMM

Set: None

Locator: JDIMM2

Bank Locator: Not Specified

Type: DDR3

Type Detail: Synchronous

Speed: 1600 MHz

Question 1: Is it possible to add 4+8= 12GB configuration in this Laptop?

Question 2: Should i use DDR3 instead of DDR3L RAM in this Laptop?

Question 3: Which RAM is best supported with this Laptop, Kingston or CORSAIR Vengeance?

Note: I am using Ubuntu on this Machine.