Three questions about RF design

I have doubts about some RF question.(see attachment) if you find it interested would you answer my 3 questions?
q1: What's the purpose to put so many vias on beside along the track?
q2: Why the bottom side (see picture) pour a wide copper plane and exposed to air (no solder mask)?
q3: By maintain 16mil track line to achieve 50 Ohm impedance , what do we need to know?
Hopefully someone can help me.
Yours sincere aid is my great pleasure and honor.

A1) these vias are to make the island beside the track are connected very well to the ground , so this transmission line is very good coplaner one , with very good stable Z0

A2) there is no need to but a solder mask , coz it is ground , and this should be connected to the heat sink or so

A3) u need to know the er of the board , its thickness , the copper thickness

khouly