I agree with Ron (for once, eh?). Resin ship kits can sometimes be intimidating, but in the case of the Johnston (or any of the Yankee Modelworks DDs), if you can build the the Tamiya Fletcher, you can build this kit with no troubles whatsoever.
The primary differences between resin and plastic are few...
Resin kits don't require extensive parts assemblies. The turrets, gun directors, funnels, etc., are all generally one piece. You clean the pour sprue (same as cleaning an injection-molded part) and you're good to go.
In some instances, instructions in resin kits tend to lack the detail of their plastic counterparts. In the case of the Johnston kit, the instructions are clear and concise. If you've already built the Tamiya kit, then you have a working knowledge of the class.
That being said, I wrote a book on the class (Warship Perspectives, Fletcher, Gearing and Sumner Class Destroyers in WW2), so if you need any help, please don't hesitate to drop me a line.
Jeff