Hey Fria, I don't think you will have any issues with sizing. The Exterior dimensions are scale for women but, the interior is very roomy. I wear a Boba Fett 1:1 + scale helmet (almost 3" wider than the Night Owl overall) and I can easily put the Night Owl on with room for padding. I know you had commented on my post about "The Owlet". No worries there, you're not getting that one (that is avery small scale for young kids like 4-8 years old), you're getting the regular one 
As for the RF... you would probably want to check with your GML and (if you plan to join there as well) the Personnel Officer at Mercs. Since there are no lights in the references, it likely may not be an approvable addition to the costume.