Yeah, that's how I feel too. I'll try my best to build and adjust it, and only after that decide if I'd be better of looking for another frames. I just got the cranks today, and I'm about to take some pictures of the Rossin in said mockup configuration to clarify the proportions. I should probably also measure it's top tube for reference.

I'm not claiming to know much about bike sizing or fitting, so I have no idea wether a 47 or 52 cm toptube would be better for me. I would guess handlebar and stem reach also play a part here? I've never had a bike with drops, so I'm thinking of a swept back "comfort bar" with a modest rise, or maybe one of those moustache bars with frop levers at the bends, which would stretch out the position quite a lot compared to say, north roads, right?