don't actively pursue the technology that would allow me to get at the tech for mansions
which are, I would assume, a pretty good building for getting kittens?
At your stage of the game, mansions are "good" for an extra several kittens before you reset to get the extra paragon for your next run. If you're looking to "power up" and be stronger, mansions are not a good way to accomplish that. On a first reset, they're better thought of as a thing you pour your last bit of resources into before you reset.
Also, mansion construction requires titanium. If you don't have trade ships, and therefore haven't unlocked the zebra trade, and therefore don't have titanium, you won't even be able to build them.
Absolutely get a couple steamworks built and leave them running
Overnight, sure. While actively playing, remember that steamworks heavily reduce coal production. Be sure you're ok with that before you simply leave them on all the time.
If you just want the 10 compendiums for architecture, it's probably more time/resource efficient to simply switch your woodcutters to hunting for 20 minutes or so and send them out to gather fur every time. So long as your culture production is at a reasonable level, this is
much faster than building up a bunch of steamworks and afking for days.
What do unicorns do
Unicorns do a great many very interesting things, including unlocking entirely new-
early on
...oh. Early on they give you a 10% happiness boost for having at least one and that's it. The unicorn "tech tree" is on the religion tab and is unlocked by building a ziggurat, which you can do any time by building a megalith from your workshop. But to actually benefit from pursuing that tech tree is a fairly long process and it's unlikely something you're going to be able to do on your first run or two.
1) It requires a lot of blueprints to build a useful number of ziggurats
2) Unicorn production benefits from relgion/paragon/faith, and if you haven't developed these to significant levels your production value will be too low to do very much with
3) Even if you're willing to put in the time, some of the things on the unicorn tree, like black pyramids, require paragon purchases. Which requires that you have reset at least once, and realistically a couple times.
So don't even worry about unicorns for your first couple runs. Build a ziggurat, look at it, get a feel for what it does, but unless you've unlocked black pyramids and are willing to spend enough blueprints to build a 25 or so ziggurats and then a bunch of sky palaces and do a fairly long run after having done all that, unicorns are unlikely to benefit you very much.
You can get some extra ivory by getting ivory towers, and that's a thing you can realistically do with unicorns on a first or second run. But I haven't generally found ivory to be in short supply, and there are probably better things to spend your blueprints on.