Is this what you want. Out of stock but might help. https://www.petersspares.com/hornby-x9653-lord-of-the-isles-loco-boiler-dome.ir or this https://www.ebay.co.uk/itm/TRI-ANG-LORD-OF-THE-ISLES-BRASS-SAFETY-VALVE-S5931-BOILER-DOME-X9653-GD-CDN/124397661294?hash=item1cf6adac6e:g:N4YAAOSwbWlfjwv5
Are they higher, maybe they are but if that is the case they wouldn't couple with older types, which they do.The prong under the hook is usually the same distance above track level. Tension lock couplings shouldn't uncouple under tension. Then NEM socket us higher on some rolling stock but then a stepped coupling is used to level things out. Over the years I converted all of my rolling stock to narrow couplings.
I have always found the cheap sprung uncouplers work a treat as does the home made piece of springy plastic. None of these things work on my layout now. 3 link couplings are a bit of a pain but look good.
Because they provided it for us. They occasionally look at the wishlist section. Adam the previous administrator told us that Hornby would not get involved with it, that is why it is moderated by the members. They would be inundated with questions if they took an active part. Why is it assumed by some that Hornby don't care? You can contact them direct using the link at the top of the forum.
To solve the problem of points warping, add a track pin as near to the centre as possible. Works a treat. When I had an OO layout even the tiny 0-4-0 Peckett crossed points slowly without a stutter.
Better to use your imagination. Sketch out what you require, e.g. track circuit, turntable, goods sidings, station, engine shed, treacle mine, rabbit factory etc. Then start getting some track on the board, very therapeutic.
Putting the platform in water? Not very good advice particularly if the platform is made of card. What if it isn't easy to remove from the layout. Does seem a bit drastic. Ordinary PVA will unattach itself from plastic without leaving a mark. 😉