I really like Brown Malt as well. I have only used it in Porters but it really does seem to bring a nice toasty, chocolate character that is different than when using chocolate or other roast malts. I would say .5 lb would be a starting point, especially for a Brown Ale/Lager. But I don't think a full pound would be out of place, especially if it was bringing the malt bringing the toast/roast to the beer. FWIW I use a full pound in a Brown Porter, along with a mix of Pale Chocolate and regular Chocolate Malt.
I was going to add, since you are looking to do a hybrid beer have you thought about using the 34/70 at lower ale temps? It's the same strain as the liquid Bohemian Lager strain which does really well around 65* for something a little different. Just thought I would throw that out there.