I tend to aim for a 'grand plan' of my fort, and plan (and adjust my plans) the operation of the running fortress towards that. Occasionally along the lines of 'Eldritch Architecture', but usually far more straightforward.
Back in the day (pre-caverns), I had a penchent for "negative building"; quarrying out all in big a hole in the ground
except the 'buildings' (pyramids and obelisks, often, but other features with perhaps a heavy
obvious influence), with the aim of absolutely
no constructed walls/ramps except (maybe) electrum 'ramp' tips to the pointy structures.
You do, of course, need to couple that with something like a perimeter wall all along the edge (design changed as the game's enemies changed), and/or a seperate dug-moat, to prevent (e.g.) enemy ranged-enemies getting a perfect opportunity to be troublesome, and I tend to fall back to more mediæval style for that (but with subterranean entrances into the various corner/mid-edge towers and sally-forts, as the inner edge is generally an even larger drop than the outer one). Ingress/egress is by drawbridge-controlled pathing in from the 'non-fort' outside, often at least four (compass-point) or eight (compass-rose) independently controllable sally-gates, plus internal access to the bottom of the (dry-)moats for rescue/recovery/retaliation purposes.
This design philosophy then transitioned into the "crossroads chasm" idea, the surface infrastructure being four walled (and, later, also rooved) enclosures set square around a controlled set of 'roadways' meeting at the centre (perhaps with Depot upon/accessible from that crossroads, in its own four-way-sealable structure). The roadways are surface-level but often mostly (retractible) bridges between natural ground 'pillars', being viaducts across a multi-Z dug void below them and around the other walled enclosures. Sufficient lever controls are linked up to open and close (and, if necessary, 'disappear' from underneath any troublemakers that I've allowed to get just so far) the bridging-roads and drawbridge-walls, plus any pillbox-like sallyforts as I have set up. (I also occasionally have 'suspended belly-gunner' pillboxes built above the routes, accessed from an upper (enclosed) gantry through one of the methods of construction that I won't go into right now. But I usually spend much time training marksdwarves and then hardly using them, with my defensive architecture alone doing most of what I want, so protected firing positions are aften more trouble than they're worth.)
Belowground, I'm still very much tending to plan my fortress plan by 'ten-tile' room definition (actually 11x11, but from the old shift-cursor jump-by-ten selection), that can split into four 5x5 rooms, six 5x3s, nine 3x3s, ten 1x5s as sub-rooms, in a corridor system between/around them that is 1-, 2-, 3-, sometimes 4-wide. It's my subsurface 'grid' that generally dictates the exact surface template to build-up/dig-out. And I generally increase the count of inter-cavern layers, just to have more uninterupted bedrock to expand into (and to create my surface chasms), skipping past the caverns themselves (at least as far as room-blocks) on my way down to the plan-consistant magma-working layer.
Working with water is probably my most intensive effort (whatever drinkable supply there is, surface or cavern, needs piping into dedicated well-dipping areas that need careful integration into the Grand Plan beforehand), and setting up the magmaworks next most (usually more a singular setup, with magmaducts to dig out and protect
before actually tapping into the supply). The possibly relentless surface/subsurface digging (and surface construction) is something I pretty much do on autopilot these days (fell trees/gather plants that are in the way, set up temporary wooden walls from any spare logs, do quick 2Z ditches at the perimiter and initial bridges, all while sending plan-compatible stairwells down to establish what rock/voids exists below, choose a "fort rock" that will be my signature surface material and get sub-/on-surface farming and pasturing allocated/reserved; all jobs that can be started with my starting-dwarves, surprises from the first migrant wave onwards might mean changes in priorities as I have more options open).
...but this is all a "I know what I like" and from a long history of fine-tuning my playing style to react to the evolving game (or anticipate it... I was building 'climber-proof(/resistent)' defensive walls before I actually found it necessary, and I think I might also have sapper-resistent architecture in hand, ahead of any need). I'm thinking that I've significantly drifted away from the "try and describe what a player of 5 months can do next", that I started off intending this post to be. Use your imagination (and not so much of the design 'ruts' I tend to base my own megaprojects around) and find your
own solutions to turtling/non-turtling and everything from the basic existence of the fort (my username is based upon my unfortunate early tendency to forget about the food situation, until too late!) to the grandiose plans for purely aesthetic/esoteric architectural elements. I still learn new things, all the time, even if I have other complex things (building upwards structures safely from inside, flood-safe hot'n'cold plumping, map-edge isolation barriers..) working almost from pure instinct.
Always more to do (or improve), though.