Hi Chandon,
Looking at your plan, for the most part I can see you can provide natural light from the rooflights as you note. The area where light may be limited, as far as I can determin from your plan, is the floor area after the island containing the sink & hob etc. This I think is where you are in the existing dwelling ?
If so, there doesn't appear to be any natural light from windows anywhere in this area as far as I can see, I guess there are restrictions on this side ?
If the above is so, then some additional natural light may possible in the form of borrowed light from the hallway, as it looks from your plan you have an open plan study area with a window. As a consideration, perhaps an inset area of glass located in the dividing wall between the hallway & kitchen would provide some light ?
Other than that & subject to what is above the kitchen area, (first floor rooms ?) one of those light tubes may be possible to duct in if it can be located without detriment to anything above.
I've a HOUZZ page with built projects & photos you could have a look at & recall a similar project, please see link below, I trust this may be of some help.
https://www.houzz.co.uk/hznb/photos/rear-extension-charles-hankin-close-ivybridge-contemporary-kitchen-phvw-vp~49547904
In the meantime, good luck with your build project.
Q
INputs from expert
Q