Re the couplings. In the 3 years of being in o gauge I sometimes find the couplings just as annoying as OO gauge.
We have Heljan who's links are formed of flat bar yet the opening on the hook makes it difficult to couple to Dapol who's links are formed of round bar.
If you look at the couplings on Heljans dog & cat fish wagons the couplings are of a slightly different design still.
I use either a magnetic screwdriver which just holds the first link allowing me to drop it on the hook, or a bent wire attached to a small torch depending on what I'm coupling.
When you factor in getting the bent wire caught on the various hoses it does test your patience.
The above YouTube uncoupling clip seems OK provided you can get in at that angle. Scenic items and adjacent rolling stock may prevent otherwise.