As and when you go for "city building," then, you may discover these things anyway.
Without the Therapist (or other plugins), you can probably still operate well enough with your initial 7 characters, popping into their job/thoughts screens and remembering who does what/is good at what/needs what/etc. Or jotting these things down (the less transient aspect) on paper, a text document or a companion spreadsheet of your own devising, while periodically checking the more volatile aspects manually (and updating accumulated skill levels, etc) as part of your playing strategy. Some things are obvious ("...has become a <profession>" alerts might mean they're now worth updating youself on, any dwarf finishing various types of Strange Mood ought to now be Legendary, the birth of a child means one extra (placeholder) person to remember, arriva of immigrants means a whole lot of (variously useful) new characters to consider the skillsets of) though others are a bit more subtle and take experience (and/or luck) to observe from an overview.
And when assigning/deassigning job-types, once you get a screen or so, keeping track of if any dwarf is currently a mason (perhaps wondering why no one is being masonic, despite something for them to be masonic with) or wondering exactly who might be better not refuse-hauling, that's when notes of some kind are useful.
DT does a lot of this for you. The 'noting' part, by importing data straight from DF in a grand table (and more!) that can be sorted to find problems/opportunities, and furthermore can be quickly changed with things you might have to dig in menus for in DF (primarily job assigments, but also nicknames and other details) that then can be exported back into the game.
It's an aid, and a useful one, but you'll probably want to play (and lose?) your first few fortresses without relying on it, at least in the early game, to fully appreciate the whole gamut of wishlist items that have been included in DT because of their absence in DF.
With LNP, you'll also have DFHack. This gives a whole range of other capabilities (and support for in-game 3rd-party extensions), from Therapist-like organiser/assistance displays that make up for similar shortcomings in the vanilla DF, to outright cheats which can make things very easy (or, if you are wanting a challenge, very hard), as you may or may not know from your Adventuring if you have delved into the tools that apply there. But, again, I'd suggest you need to see "normal" gameplay and understand how you'd (e.g.) mass-dump items, organise stockpiles and convey liquids from A to B before automatically jumping into the additional tools to do those things without so much hassle. (Hassle is part of the achievement, naturally. Even in failure, which is of course a learning experience!)
((That's basically my "long" explanation, yet misses so much detail out. And I realise I forgot to welcome you, also, like I had intended to in my first message above. Enjoy!))