1, Yes, turnbuckle = 'fine scale coupler'= 'model coupling' [ in German ]. I've not operated that coupler on curves less than 32"radius, and even that requires excessive distance between buffers / cars.
2. Your -2 loco [ = scale wheels ] requires [ according to MTH electrons ] a 31" radius minimum curve. The -1 [ = tinplate ] version can go around a 31" diameter curve.
3. I don't understand the "box car" with a knuckle coupler thinking [ see my para 2a above ] -- unless you are planning to change / modify the TP wheelsets to scale standards. Are you using Peco Code 124 or Code 148 track -- I presume the former, for a French look. The sample MTH boxes for Euro cars I just looked at say nothing about min radii.
Confused, SZ
