I would recommend getting a Mixing Ratio mixing cup , or a granulated mixing stick , to mix your product .
It kind of depends on how much area needs to be sprayed , & its hard to say how much you will need as some painters lay heavy coats and need a little bit more , some spray light and need less , plus it depends on your gun settings And the gun type used , as HVLP will use less material , then the old conventional siphon gun .
I would mix little portions at a time and see how far each mix goes , if you need more you can mix a tad more to finish , instead of pouring it out .
The more you spray the more its easier to figure out .
DPLF is a 1 coat sealer and will require less product mixed then K-36 , I would mix 8-10 oz's of DPLF for a hood and fender , that should lay 1 coat.
On the K-36 I would mix a pint , and count how many coats you lay with that , and this can give you an Idea on how much will be needed later on .
And yes you could spray any extra on the interior as long as its been scuffed !
Use PPG's DX 330 or DX 440 wax & grease remover , the 440 is more aggressive , I use the 330 for my wipe downs .
I know I wasnt able to give you a true Mix Ratio Guide , but its hard to tell someone how much they need with out knowing how they spray , as I spray my coats on the heavy side so I require more :-)