Hey Ron,
You're not going to run into any snags building the Fletcher...or working with the GMM set. You will run into an issue with the Fletcher turrets, as they're badly undersized. L'Arsenal and White Ensign Models do aftermarket turrets, and Corsair Armada is releasing an INCREDIBLE set of turrets shortly (I have a review sample).
With regards to paint, you have two choices. You can paint the ship in Measure 21, which is overall Navy Blue 5-N, or you can paint the ship in a variety of Measure 12 Revised schemes (this is the pattern you see on the box art). Many ships were commissioned in Measure 21, repainted into Measure 12 Revised, and then repainted back into Measure 21 before receiving any refits.
You cannot paint your Fletcher into any of the Measure 31 or 32 dazzle patterns without upgrading the 20mm and 40mm fits of the ship. Tom's Modelworks does a square bridge conversion kit to change the bridge structure and add the additional 40mm to the kit.
I wrote a book on Fletchers, the first of the Warship Perspectives Series, so if you need assistance, design sheets, or detail shots, email me and I'll see what I can do to help you out. In the meantime, you can visit www.modelwarships.com and check out some of the Fletchers in the gallery.
Best,
Jeff Herne
Modelwarships.com