I think I'm going to say no to all combat-oriented ideas. This is a retirement center, for rest and relaxation. I don't need to entertain adventure mode players, just give them a nice destination after they've completed their trials. I'll have to add in a hospital I guess for general upkeep of all those old wounds. Some of the dwarfs from the construction crew will have to stay as doctors - is there any way to directly hack the skills of each dwarf? I don't see a way in DFHack. I want to just finish this retirement center as quickly as possible, then hack each of my dwarf workers to have the skills I want and leave them there to cater to the retirees. A doctor and a couple of nurses, a cook and a brewer, etc. - all with legendary skills (which I don't want to have to build up manually, especially the doctor). I'll also make a few legendary soldiers which I can then take on adventures to be the first retirees.
By the way, the center is located in a fortress with serene surroundings. There is sand for glass and an aquifer, chosen so I could easily make the swimming pool. So a waterfall will be possible, but I have almost no experience with water projects. I'm not even sure I've ever used pumps for anything. Can someone provide me with (or link me to) a quick guide on using an aquifer to create a waterfall area without flooding everything? Just have it drain into the caverns? Will my dwarfs work underwater (in the aquifer itself) if I mod the raws so they don't need to breathe? That would speed things up a bit. If it's too complicated I won't bother though. I'd really rather get to the succession game than spend a lot of time making fancy additions to an area that won't really be used.
So far I have the humans' apartment building done but unfurnished and have mostly finished the gallery, and I'm finishing up the swimming pool area (with some tables and such around) and definitely planning a small wooden apartment building for elves and an underground area for dwarfs. Anything else I really need? Or maybe I'll just leave it at that.