Supersize everything you have planned by making the floors 4 z lvl high each.
Urist McHauler does not need a 4z high living quarters.
1. A safari park with one of every animal in the entire world in. Not a zoo with them all in cages, but a single level for them to roam freely in, and some glass walkways for dwarves to come and gawk at all the weird and wonderful animals.
2. A hall of records filled with row after row of cast obsidian walls all covered with engravings, and with the mechanics set up to make more walls once you have covered it all.
3. A vault that takes up a whole level in which you place all the artifacts and other shiny things that you dig up and make.
#1 I like. I'm gonna go a step further though and try to introduce some ponds, as well as a few enclosures (accessed from the walkways above) with windows for ground-level observation.
#2 is... unfeasible, due to the fact that it does, in fact, require infinite space in order to build a continually growing tower of knowledge. I do like the idea, though - I think I'll try to find a volcano and a river on another embark and make a giant obsidian Tower of Knowledge. I can do this with any kind of exploratory mining I do in the future, though.
#3 is something I was kinda planning on anyway. Things like jewel-encrusted gold/platinum crowns, figurines or kings/queens of this civ, masterwork golden armor (which was the one thing I have modded in, gold and platinum equipment - because after all, those nobles should have a set of suitably fashionable and expensive dress armor for when they lead troops into battle...), masterwork weapons, artifacts, large gems, and that sort of thing.
Since t's a mountab ho9me, it needs accomadation for proper number of dwarves,
I'ld go for: (*but you won't, since you've already got this covered)
basic accomadation (for say 500 dwarves...) as (over three layers)
[...]
From dwarven luxury and relaxation suite - for maxium rehabitation a enjoyable attmoshere is advised. complete with platinum table, throne, masterwork engravings etc.
Ranging down to hell suite: floored with grates, looking down on the the schorching lava blow.
at a pull of a lever, water falls from the ceiling (conviently washing way any ... stains), into the lava below, sending plumes of scorching steam
You know, I really SHOULD plan to house a ridiculous number of dwarves. This is, after all, going to be THE mountainhome, not just some ordinary fortress. I can get a bit over 100 per floor with the pattern I have right now, so 4 floors should give enough space for 450.
As for luxury suites, yes. Those are called Noble Quarters. I don't think I'm going to include hell suites, though.
EDIT:
Current plan for the magma tombs - feedback encouraged, I don't want to have to rebuild it. Magma drops down directly into the big tomb, and passes through those tunnels to reach the smaller tombs. I'm also toying with the idea of instead, using a small 'lava chamber' between the tomb and the entrance door (so you would have hall -> door -> room with lava -> door -> tomb) so it's TECHNICALLY accessible... if you're willing to sacrifice a dwarf or two.
Or constructing it so that the magma tombs can drain into the noble dining room