So here's the question: if you could suggest a progression for someone who's interested in eventually  building (and flying) giant-scale warbirds, what builds/kits and in what order would you suggest them to build skills and flying confidence to get from zero to hero?

I'm thinking of going from a small-scale kit (to make sure I really want to build, and not just to fly) to a Sig Kadet Mk. II or LT-40, to a Four-Star, to maybe my first scale model (a J-3 Cub or a similar fixed-gear GA plane) to... I don't know what? 

Thanks, all, in advance for the warm welcome and for any suggestions and information you can offer!

That's an interesting question.  I'll go first (as a fellow SoCal guy, but currently living in Japan).  I suggest taking a 2-track approach:  One for flying and the other for building.

For the flying track: Get an AMA membership, find and join an RC club, buy a cheap trainer ARF (not a foamie), and get one of the skilled pilots at the club to get you started flying on a buddy box.  Done this way, you could be in the air in as little as 2-3 weeks.  You could be flying solo in a month or so.  Actually, assembling your ARF (Almost Ready to Fly) will provide the first few steps in becoming a builder.  You'll learn how to install a motor and radio gear, how to work with epoxy, how to do linkages, and how to do all the other little tasks that are a part of every RC model build.  

Meanwhile, for the building track, get one of the kits you mention (any of those would be fine) and start learning how to build..and collecting the small number of simple tools you'll need to get started. 

Regarding a progression, high wing (i.e. shoulder-wing) models are considered easier to fly so most trainers are set up like that.  Once you can fly your trainer reasonably well, you might move on to a "scale trainer" like a Cub.  A Cub (or something similar like a Taylorcraft) will teach you most of what you need to know about flying, including how to really use the rudder. 

The next step towards a warbird (I assume you mean WWII warbird) will be a low-wing model.  There are several low-wing semi-scale ARFs available (such as the Spacewalker).  Personally, I'd stay away from the nice looking WWII warbird ARFs with the pre-printed surface details because you'll never be able to repair one.  I'd stick with 50-engine size models until you're an intermediate flyer (no sense cracking up an expensive large model with an expensive large engine).  Accept that you WILL crash a couple of models.  We all have.

One thing about WWII warbirds, for the most part they have retractable landing gear.  Good retracts typically cost several hundreds of dollars...which is one reason I build WWI .

And eventually something like this!  Something to dream about for now...on the other hand, you can also buy a kit for the future since it seems to be a fact of scale modeling life that any kit available today will not be available down the road.

https://www.fokkerc.com/product/messerschmitt-bf-109-e4-15-s cale-model-wooden-kit/

Good advice from Ed.  But start in on both the flying and the building at the same time.  Otherwise, you might spend 6 months (or more) building a "first model" before you ever start flying.  And there is a VERY HIGH probability that you might crash that first ever model within the first 2-3 months of flying it. Been there, done that.

Back in the "good" (or "bad") old days, the only way to get flying was to build your own model.  That's fine, but it will delay your learning how to fly by many months.

A month for a newcomer to build a Cub from a kit?  Maybe if they are working on it non-stop for several hours 7 days a week.  I built my Flair Puppeteer in six weeks, working flat out every day.  That was really throwing it together with few embellishments. Maybe the SIG Cub goes together faster.

But I agree with Ed that in a month of weekends (if you can corral your instructor for all those days) you could be ready to solo. 

In the end, all of this depends on how much time you can commit.  Are you still working...or retired like many builders here?  Do you have kids or family that occupy a lot of your free time?  How often can you get out to the flying field? (For most in SoCal it's a 30-40 minute drive each way on the freeway.) 

Get something quick and easy and start flying if you arent already. Build a Cub, which you can throw together bare bones simple, or take the time to add the "scale" components and learn. Maybe a Skywalker or similar. Then I would suggest trying to find one of the Top Flite Gold edition 60 size warbird kits. They were well designed and relatively easy to build. But would be a good introduction to building larger, more complex warbirds from plans. And get you competent with all of the relevant systems required in such an airframe. Advanced radio install and setup, retracts, dealing with the air system for the retracts, you could add scale lighting. Nothing is more frustrating then spending hundreds of hours building only to be foiled and delayed or have to back track to fix a leaking retract air tank. 

Oh and go through the shop/tools threads here. You can assemble a basic kit with some basic hand tools. But to get to that next level there are many tools that will make the job more enjoyable as well as more successful.