Where can I learn more about the technology background of the universe. I find it odd/interesting that people seem to live in a D&D level fantasy setting (Wooden ships and crates) yet have iron bunkers and iron magical warmachines, yet also still have a lot of flintlock looking weapons, cross bows mixed with tanks.
Also with all of the flying warbeasts etc, why have the factions not developed magical flying machines to combat them etc?
The most in-depth background info on tech would probably be the RPG books, either Requiem or the 2nd edition books. Otherwise a lot of the faction books from Mk2 or Mk3 would have some of this stuff, but I think it’s most concentrated in the RPG books.
To answer your specific questions:
Firearms and fantasy - One thing that is easy to miss with the IK setting is that they don’t use gunpowder as we know it. “Blasting Powder”, which is their equivalent, is actually a combination of two powders that combust when they interact. The two powders are stored in paper bags that are wrapped in a larger paper cartridge with the bullet on one end. Pulling the trigger causes a spring-loaded pin to pierce both bags and cause them to mix and combust.
This is significantly less powerful and less reliable than real-world gunpowder, resulting in firearms that have much lower force and accuracy than equivalent real-world weapons. Thats why you still see plate armor showing up as a viable protection against most firearms; they simply lack the penetrating power to consistently pierce steel plate. It also means that crossbows and longbows are at less of a disadvantage to firearms when it comes to range and power. Also storage is a big problem because literally all it takes for the powders to ignite is physical contact, so even something as simple as storing the two powders in nearby barrels becomes problematic if the barrels start to rot or are damaged and leak even a little bit into a shared space.
As for flying machines, they actually do have skyships as of about 10 years ago in-universe, but these are massive vehicles that are extremely expensive to produce so as far as we’ve seen they’re limited to governments. You can see a couple in the cover art for Requiem at the bottom of this page: Iron Kingdoms: Requiem - Privateer Press
As for smaller airships, would you want to fight a giant bird that shoots lightning from an airship held up by hot air? Basically it seems that until they figured out the technology behind the larger skyships going up in anything less durable was just too much of a risk.
Adding to what SaltTitan said:
It looks like the Immorese solved a lot of their engineering problems with magic, and thus they probably have some gaps that we didn’t. 
Blasting powder is magical and made via alchemy, not chemistry. (…unless something seriously changed in Requiem…)
They have super-efficient steam engines because they were invented something like 1,100 years prior. The technology flourished even during the Orgoth occupation.
The setting itself is well beyond standard D&D fantasy levels of technology. The industrial revolution happened centuries before. People live in vaguely Victorian-era cities. Train networks exist. Telegraphs exist in Cygnar. Warjacks exist because 400 years ago some bonkers crazy wizards and engineers got together and said “Hey, it would be a great idea to build 200-foot-tall robots so we can throw off our Orgoth oppressors!” and then did it. 
They went down that particular technological rabbit hole and that’s how we ended up with the current warcaster + warjack paradigm we see today.
(Note that there’s nothing that says the real world had to develop the way it has. We got here by happenstance and circumstance. Nothing’s ever going to evolve exactly the same way.)
To be fair, we still use wooden crates today in the real world.
The short answer there is: Caen is a very dangerous place. Are you gonna fly in an unarmed blimp when dragons exist, when crazy, strong weather patterns emerge due to Caen’s three moons and huge tides, and where any random flying monstrosity or magic-wielding pyromaniacs can come by and bring you down?
That is all really awesome. With the books not something you really see around are their any plans to add this lore type stuff into the app for us newer players?
It’s certainly possible, there’s some already about Storm Legion and Orgoth warjack tech. But the Requiem RPG books are certainly still for sale so those can be a resource as well. I believe @ServantOfNyrro also has some good background videos on their YouTube channel that covers some of this stuff.
Here’s Servant of Nyrro’s YouTube channel: Servant of Nyrro - YouTube
Couple videos that might peak your particular interest:
Ruling the High Seas [Navies]
Welcome to the Iron Kingdoms
Thank You! I will check this channel out