I agree with Davro regarding ditching the Kevlar. Remember that Kevlar is only stronger than carbon once the laminate has failed, so if it is in the layup then it's only there to hold things together in the event of failure. Overall impact resilience comes from the stiffness of the laminate, so it's better to make the laminate stiffer to resist impacts which means carbon is the better choice. S-glass fibreglass would actually be the best choice for impact resilience and overall laminate strength.
If you are worried about penetration then perhaps a small amount of Kevlar to protect the driver from anything coming through the floor, but keep it localised.
Davro would know more about these kit cars than me, so his suggestions are probably good. I have built floors for Stohr F1000's, which may be pretty similar. These floors are generally 2 layers of fibreglass with 15mm honeycomb in the middle section and 10mm divinycell in other areas like the rear diffuser section and sides. The areas with no core are 5mm solid fibreglass. I would look closely at that layup and save a bit of weight/thickness by doing it in carbon.