Terrified to start

Hey yall, i need some advice or encouragement.

I bought a custodes combat patrol because i wanted to get into assembling and painting the minis, i used to have some imperial knights but sold them after they gathered dust and never got painted.

I want to paint these custodes in a sort of "Arlecchino" color scheme, Whitegold (Chrome), with black and red detailing, but with no experience whatsoever painting im terrified to begin, as im realizing just how many small details are on these models.

How do i paint the eyes without hitting the faces?? how do i paint the blades of the guardianspear without hitting the gun?? how do i paint edges without smearing the sides??

The minis are getting dusty just sitting on my desk and they deserve better. i dont know how to start, im terrified they will look BAD