I don't know if it's inside the scope of a starter guide but it'd be nice to get some general info on the different types of soldier you can get and their different use cases compared to your average gal. Things like where does an ogre fit in to your squad, or how do lokk'naar compare with gnomes as the only tank pilots everybody gets. Are there soldier types I should definitely focus on keeping alive and growing, or can I just mince my blood hounds? Who should be piloting my fighters?
Funnily enough, I was umming and arring about adding a section with this in.

That's to say, covering the types of troops not given directly by the routes themselves. There is a lot of differing opinions on this one, which is why I've not put it in yet. But then, the bounty prize section is also quite a bit of my opinion, so I guess I'll consider adding it with a disclaimer like that.
So, these are my quick takes on the ones you mentioned, some of them might be considered hot takes, I dunno.
Gnomes: They're small sized, so you can take them underground. They have massive Stamina, so that means they can and should ALWAYS be CTRL-Clicked to Run everywhere (as a result, their low TU isn't as low as it seems). They are unbreakable (spawn with 160 Bravery as a MINIMUM) and basically immune to Psi and Mind Control, and themselves make excellent Voodoo users. Moreover, they have unique armours that are generally superior to whatever your Gals are using at the same tier from the same tech (i.e. whilst your gals are in Heavy Tactical and your cats are in camo, gnomes have plating with energy shields). Similarly, you can get Gnomediscs way before actual Hovertanks. Obviously, they have tiny Strength, so will always be using handguns or SMGs. Fortunately, both have some incredible options (i.e. Silver Snake adds 15% of Bravery and 10% Accuracy to damage: oh look an elite Gnome has 180 and 130, so that's a 60 damage revolver shot). Availabilty is the other problem- The Game considers them Hero units so they're quite rare. Which is why Blackmarsh start is very valuable. My most Elite gnome, Arya von Liebenstein, is a beast with over 600 kills to her name.
Lokk'nars: IMHO, they're the "Can we buy Gnomes, mum? No we have Gnomes at home". However, for many playthroughs, the goblins might be your only small size race. So you need some in that case for the various underground missions. I find they're handy for plainclothes infiltration missions since PUNK/LOK is a very good infiltration outfit early and you're mostly restricted to handguns anyways. If elite, they're basically between Catgirls and Gnomes, not quite as good as either specialised, but a decent hybrid. They start pretty mediocre stat-wise on recruit compared to either, though, so training your green goblins is a bit of an exercise. They're pretty good with Suppressed Pistol like Catgirls, so that's a decent pick. Squishier than Gnomes due to worse armour in general. If, for example, you're not on Catgirls route AND are not getting Gnomes, they will absolutely be your main infiltration/underground/piloting specialists.
Ogres: They are very tanky, and VERY slow. They start with pretty dreadful stats in most cases (you might have 40 TU/40 Stamina to start!), and being tough as nails doesn't mean much if you can't actually get to the frontline to get kills and take hits. Because of this, I personally don't like using them all too much. They're not even stellar at melee to compensate (and are too sluggish to get there often). However, if you
really focus hard on feeding them kills, they have a very high ceiling and a pretty great payoff for your suffering. Getting Pyroman/Roman Legionairre suit is a priority early if you use them; it's pretty great on Men, and even better on Ogres. They will likely be in that a LOOONG time, though. You can switch to Liquidator armour as stats and tech improve if you want, but then there's a huge armour gap until you get Ogre Power Armour. Barrager Armour is amazing though. Like seriously amazing.
Pets in general: I've used Cats, Doggos and Bloodhounds. What they are good for is being disposible scouts, really. You rush them in to be annoying harrassers as the AI does with them, they get killed, but if in so doing they allow your girls to take everything out, it's a worthy sacrifice. The AI hates pets with a vengeance for some reason (I've literally had a Guild Marine leap off the top of a 8 floor Comm Tower just to fire his shotgun in my dogs face once!!) so you should abuse that. Don't expect them to survive. For Bloodhounds, though, if you have a primary Lokk'Narr's they're better held on to and then used to make RIDER/LOK. Goblins riding hellhounds into battle is not only hilarious but actually really helps Lokk'Narr's be awesome for once.
I post archives of my gameplay on youtube (unlisted), some songs would even make the entire video banned from viewing because of the copyright lol. However, I seem to be able to stream xpiratez on twitch just fine
Yep, that's what I mean.