Using the same stain for the maple top as for the mahogany will result in very different colours, with the top a lot brighter. A reverse version of this 2020 Epiphone SG.
This kit is really a good candidate for a dark back and sides and a sunburst finish around the edges.
Maple veneer so you won't need grain filler on that, though you will on the mahogany.
You can use a dark stain first on the veneer, and very lightly sand back a bit to pop the grain, but it will make the overall finish darker (though that might help match the mahogany body if you use the same main stain colour all over). Use P400 grit at coarsest, though I'd try P800 to start with. You really need to be careful as you've only got about 0.5mm of veneer thickness to start with.
Do first check for glue spots using metho, as these will need to be dealt with before any staining. Wet the veneer and the top of the mahogany body with the metho, then check for any light areas that the metho hasn't penetrated, This will be due to excess glue left over from sticking the veneer on. The centreline join and around the edges are the most common places to find it. The glue needs to be removed before you'll be able to stain it properly. Goof Off rubbed on with a soft brush seems to work for most people.