You have good hand eye coordination. Rough sketching a anatomically derived shape is not an easy object too tackle and drawn in perspective view, correctly, conveys to me that you've a solid grasp observing those key features of a given subject...nice going.
The artist is either using an imported brush set or modified their own:
"I have never let my schooling interfere with my education" Mark TwainHardsurface WIP
Your sketches are fine, no need to be pedantically concerned with proportional accuracy at this stage. Drawing in and of itself is a foundational skill that'll take years too master and if character art might be your thing checkout Anatomy For 3D Artists workshop by Scott Eaton. He's a classically trained sculptor/painter, had studied in Florence plus a pioneer in digital sculpture.
Yeah, Feng Zhu is dope! I've worked through some of his tutes myself and initially found was a steep learning curve when making my first wobbly, tentative steps into the realm of digital painting. Another Concept/3D Artist you might not be aware of is Stefan Morrell, whom I have followed since shortly after jumping across too CG via the traditional space in 2006. His art is honestly eye popping as you'd expect from an industry vet.
(BTW I've had Sefan's 'Red Mech' PC screensaver 3yrs running, mainly for inspiration as a hardsurface modeler )