The screws are tiny so I'd say 5nm is about right. Bicycles use around 5nm for their stems and seat posts so I don't think you have too much to worry about for the fork brace. Remember inner screws tightened first and outer ones second. There'll be a small gap on the outer.
Also if you remove the front wheel, you may need to remove the fork brace to get the wheel to reinstall correctly and then refit the brace - I find there's a tiny gap between the spacer and fork leg if I don't.
