I have a Latitude E6430 laptop with the Core i5-3340m CPU @2.70 GHz

It came with 4GB 1600MHz RAM and this is barely enough for Windows 10 pro, so I have two questions before I buy more RAM.

First question:  is my motherboard compatible with DDR3L modules?  The Dell Latitude Memory compatibility guide says DDR3, but posts on this forum seem to indicate that DDR3L also works.  Being more recent, DDR3L is cheaper and more easily available.

Second question:  can I mix module capacities?  I am thinking of adding a 8GB module beside the existing 4GB module.  Would this lower performance compared to a matched pair of modules?  I know some motherboards do dual-channel access of memory banks.