Always set a quality bar for yourself. First person weapon? Third person weapon? Environment prop? Etc. Tricounts now vary wildly with this new generation. First person weapons will probably go from around 3,000 tris for a simple pistol all the way up to and beyond 50,000 for complex weapons.
I really love the Low Tech Feel, and there's nothing wrong with making a few adjustments that differ from the original concept to make the model a little better. Sometimes what works in 2D doesn't work as good in 3D and viceversa. I made a sci fi weapon recently and mirrored most of it. I realized some of my baking errors…