Building the perfect professional chocolate kitchen

Hi, I am planning to turn the basementof an old school house (from 1903) into a professional praline making kitchen, but need some advice regarding air conditioning etc. I know that high humidity is a big problem for the chocolate. Does anyone know the recommended percentage of air humidity in the kitchen (for ex "not more than 75%")? The climate where I live is very dry (and cold)during the winter, but in the summer it can get very hot (Scandinavia). Is it generally a bad idea to build a praline kitchen in a basement? I have plenty of windows.