Click on the link I posted above for the Tobacco KML. There is a suggested % for use in recipes, a range, the average and the median %. Some of the notes have what people have tried. I usually start with the median %, and adjust from there. Then click on the vanilla flavor anyplace you have seen it, recipes or flavor list, and find out what it's median use in recipes is. And those could be a starting point for each.
It's going to take making small batches to determine which %'s work for you.
Because of the steep time, I would make a few small bottles of different options with different %'s of the flavors all at once. Let them steep using your preferred method. Then try them and see what tastes best for you.
Make sure you keep notes. Label the bottles with the date mixed, nicotine mg, % of PG & VG, And which version of the recipe is in the bottle. (ie...3.5% tobacco, 3% vanilla, but with your actual numbers) or name them Version 1, 2, 3, etc... and keep a record of the exact measurements used in each. I save them as recipes on here, it's convenient!
Just be sure to make new recipes for each version, don't edit, because it will save over your last one! Learned that the hard way! Lol!