Cygnar Starting Guide?

It's all about whether you want to go casual or competitive. If you want only the most powerful, I'd go with some variant of Haley2 / Sloan / Nemo3 and leave out Haley3 to start because apparently she's quite challenging to play well. Personally, I avoid Haleys, so if you're looking for list recommendations and purchase recommendations, I'll offer the following:

You don't appear to have any lancers, which if you're playing in theme you'll want with many casters. Only Haley can bring Thorn in theme. Also, if you want to play out of theme, consider Gibbs for Stryker2. If you play Caine2 or Sloan, you'll want Reinholdt. If you play Nemo3, especially with the battle engine CID, consider a Storm Strider.

Here's a Stryker2 sample list I just whipped up based (mostly) on models you own.

Stryker2 (Theme: Storm Division)
Squire (free)
Ol' Rowdy
Lancer
Stormlances (max)
Stormlances (min)
Laddermore
Stormblade Captain
Jack Marshalled Stormclad
Strangewayes (free)
Journeyman Warcaster
*Firefly

The stormclad jack marshalled to the SBC with Arlan is insane. I wrote an entire article about it here: casualty-wmh.blogspot.com/2017/04/module-stormclad-stormblade-captain.html

Personally, I love bringing 2 units of Stormblade Infantry with Stryker2. With arcane shield or iron zeal, they get up to ARM20 vs shooting under deflection. With both, it's ARM23. Trouble getting them delivered? Nope. And when they get there, you try to get positive charge and ragman into place, and a firefly within 5". Then each one of them gets a POW18 assault shot (POW12 +2 from the leader +2 from ragman +2 from firefly) plus a POW19 charge attack (POW13 +2 from the leader +2 from positive charge +2 from ragman) - this means that against an ARM20 colossal, you're looking at 14-15 damage each from the stormblades. Four stormblades can wreck a colossal this way. Too bad the ideal scenario pretty much never presents itself - getting all the buffs in place isn't always that easy. But Stryker2's feat helps a lot.

I can give you another couple sample lists if you're interested (maybe Caine2 or Nemo3) but no time at the moment. If you don't want to proxy and use Thorn for your lancer in the above list, maybe play Stryker2 out of theme and rejigger the list to bring Thorn. Having the arc node for Rebuke is really nice, and it's good for getting positive charge in place as well.

Welcome to Cygnar and congratulations, you already have most staples to play so you won't need to buy much else.

As Gmonkey said, the first thing that you seem to want is a Lancer. Until this year you could do well without it simply playing Thorn with every caster, but now Cygnar is pretty much forced into playing in Theme (either Storm Division or Heavy Metal), so you need a non character Arc node.

If you want, you could also grab the occasion to get an MK3 battlebox, that is very cheap and, other than the Lancer, will bring an extra ironclad and an extra Firefly (and you could actually play 4 fireflies in some Nemo3 lists), and expecially would bring Maddox that is a very good caster that works well with the things you have.

About your Stormclad kits, if you are unwilling to magnetize, mount 2 Stormclads without worries... Reliant is one of our worst jack and will never see the table until they fix it.

As already said, the best casters you have at the moment are Nemo3, Haley2 and Haley3, but both Haleys (and expecially the third) are quite difficult to begin with, and the new steamroller will probably have an impact on Haley2 usual game plan (that is to play on scenario, a thing much more difficult to do in SR 2017.)

I have some doubts on Sloan. She is nice in theory, but actually months of releases and changes specifically intended to harm shooting play has left her somewhat lacking in my opinion (as an example, Shield Guard ruins her days, and now most factions have easy ways to field tons of cheap shield guards).

I suggest you to try Nemo3 for sure (either in Storm Division or Heavy Metal, depending if you want to play him with Stormlances or with tons of Jacks).

About Stryker2, sadly he suffers a bit from not having a Theme list that works well with him. Storm Division is the one that comes closer as far as desidered models allowed, but has the big flaw of not having anything giving Pathfinder allowed, and he really needs it for his game plan.
He is a very good caster per se, but the opportunity cost for playing out of theme is very high (you basically play 15 points short) and that is damaging him right now.

Let's see how the Trenchers theme forces will be, and if the hinted "Trencher Runewood" will deal Pathfinder. In that case, he could find his niche there.