P4Frank

I don't know about the Dapol system but I have used DG couplings for some time on P4 and HO and I'm very happy with them. I find they are very efficient and the occasional tweak on setting up usually ensures they retain their settings. They work well with both fixed and electro-magnets. I modify them so that the hook is at one end and the loop at the other which means they have to remain the same way round and thus not possible if you have return loops. Locos that need to run in either direction would carry normal couplings both ends. I'm sure you would find some way to fit them even on the difficult vehicles. They can easily be fitted fixed to body or to bogies.

High Knuckles, this is my firsty posting so i hope it works ok. I think you are possibly complicating things with the branch especially as it appears to only be one way. It would be better I think to make the track nearest to the station building into a headshunt, the next track a bay platform and omit the branch. The points on the curve would be possible in p4 but if you haven't built P4 points before I would do the others first to gain experience. I have a minimum 42" radius and would suggest 36" may be a bit tight. I hope this is helpful