Just chiming in to agree that chocolate is a bit odd here. It's not that you won't make a good beer, but barley wines rely on malty/caramel flavors, not toast or roast flavors. You can achieve malty flavors by using a lot of medium-colored grains, and/or by a long boil to caramelize. Some recipes even use exclusively pale malt but do a very long boil in order to get the color up. I think your C80 largely covers it, so combining that with a long boil would work. You could also consider adding some biscuit/aromatic, or some Vienna/Munich or lighter crystal.
Agree that pitching onto an existing yeast cake is the best idea. I don't think I would use WLP099; I have heard that is a very strange/inconsistent yeast (though I haven't used it), and you can use something more standard (WLP001) with good results as long as you treat it well. Just make a 1.040-1.050 OG beer first using WLP001, then pitch onto that. Two more tips to increase attenuation: start in the mid-60s but let fermentation go wherever in terms of temperature, and rouse the yeast (rock the carboy) after a few days to make sure the yeast stays in suspension longer.