Intriguing, I like the overall style. Though as a professional nitpicker I have a few observations
Is there a reason why north and south are inverted? I'm assuming this is a coastal defensive fort but the military context is unclear to me. I'm assuming the seaward side is to the left (east), with the martello tower having a field of fire in that direction, expecting fire from the southeast (top left). Are the chains protecting an inlet?
The barracks building looks a little odd as it's not rectangular, and the squared windows(?) are on the inside. The Fort James example (built to defend the mouth of the Gambia River, as I recall) makes it a bit more clear what's indoors and outdoors. I'm not keen on the inner and outer glow lines around the island - for the water it might be fine but coming inland it looks like contour lines (intended?), meaning you'd have a very flat island (not inconceivable).
The James Island map also has fortifications right around the coastline on the defended side. From a tactical point of view it would be possible tho bloody to land men on the "southern seawall" side in small boats and assault the terrace. Building defences hard against the sea prevents this but would be more expensive, so it would depend on and how strategic the site is.
I'm intrigued to see that Victorian map has shadowing - the number of times I've been told that's inauthentic on Victorian style maps! But I guess the effect is subtle there.
No slave quarters in your map? Ah, the good old days of empire...