For your initial question , I would agree, ask your dealer. The 'latest' variation, I believe is the 2014 and I know at that age I wouldn't be messing with all the magic inside
Don't know if it is anything like the L322, if it do you really want to take your dash apart to get at the system? Especially when you already have a good system.
For the second question, go sit in it. Have a test drive. Take your three adults, ask them if they're comfortable. I find my L322 comfortable to sit in but short of leg room. You would find it different. It's all down to the individual what they find comfortable
As to is there a better site for newer. The answer is no. All of these sites have the same type of members, some are clueless, some happy spanner monkeys, some electronic gurus, some stuck in the past and wont touch the electrickery models, some are absolute gurus , some have gained their knowledge from working on their own vehicles and some work for Land Rover. The one thing in common, is they are all playing catch up, as owners of newer models crop up and new problems looked at, solved and knowledge gained. No matter what age your LR/RR this is the place to be. We learn from each other and share what we know. There is always a 'first' for everything. You are just the first to ask this particular question. Whilst most of us won't know the answer, you can be sure it won't be long until one of our members does.
The fact that the L405 is no longer 'new'( just expensive for the older ones, which will change in 2yrs I expect and the bottom will drop out, as it does with RRs, as they hit 8) , having been jntroduced in 2012. I had a quick look, and considering the amount of recalls on the L405, hang around a bit and youll have others joining you.