Basically you are trying to convert it into an English Barbour waxed cotton jacket.
My advice is don't.
The results from those sprays and waxes are not that good and it takes a little practice to get it right anyway. You may or may not finish with a more water resistant jacket but it may look awful and the material won't breath so well - think sweaty. Just use it as is and buy a waterproof.
On the subject of Barbours, they smell, leave wax stains on cloth upholstery and should not be allowed in the house. (Because they were very fashionable in Italy a couple of years ago my view on the subject was considered eccentric
)