Helmet probably should be last, not first. Yeah yeah, everyone wants a helmet to drool over. But it's the thing everyone stares at so you want to do it AFTER you've developed a process, techniques and skills.
Personally I always recommend starting at the feet & hands then working up & in to the body.
• You're going to weather and distress the boots more than anything else... and they get looked at with the least critical eye.
• Then shins which have to ride on the boots.
• Then thighs since you have to avoid joint conflict so you can sit etc.
• See how this goes? Up from the boots, and inward from the hands to forearms to biceps to shoulders.
• By the time you get to the chest and helmet; the parts at eye level that everyone stares at, looks at first, is right there in your face in every photo - you can make them look stellar.
And if you start at the boots you're looking at parts that are only a day or two per part not 6 days per part. So you can hone your scaling skills.