Actually you are following the steps I did for the jelmet…
But wotk forst on the global shape of your helmet, your low res. Mive was build on a guy head, to be sure it fits.
Turn your helmet in every hangles, to be sure its rounded, here’s some good refs:


My low res had a helmet shape, with the goggles protector extruded.
I created some polygroups to hide/show specific areas. I also did some Creasings in some parts to maintain sharp areas when subdividing.
I use a lot the layer brush to have very clean lines.
You have to be patient and work slowly to maintain the better quality. I mostly use all the time the mouse average to have a smooth line flow.
Don’t forget you can mask the areas you dont want to sculpt, to concentrate more on other areas…
The shoes is not a bump shader. I got 1 gig of ram more (2gigs) so I could reach a high polycount on simple meshs like a shoes.
My low res mesh are EXTRELY simple, only a global shape, made of quads, nothing more.
Something like that:

But with more regular quads, I try to have the most squares possible on my low res, it makes a more homogen model, same details everywhere.