Hey!
This is purely subjective and just my thoughts, so take it with a grain of salt. I don’t claim this to be the only way to learn but how I learn.
If you’re new to effects, or anything, start with doing whatever the hell makes you happy. Just get in and do things. Don’t worry about your path or trajectory or where you’re headed. Splash around in the paint and get your hands dirty. But do something instead of being paralyzed by analyzing if you’re doing something right or wrong.
I assume you’ve read Getting Started in Real Time VFX? Start Here! - #35 and
Shannon McSheehan - LoL FX + Knowledge Share.
Scroll through the Resources & Knowledge category. There’s so much loot in there. Read the forums, read sketchbooks, start your own!
Have you installed your softwares and started messing around with them? Did you make shaders? Did you animate something small? Have you scrolled a texture yet? If not, then go and do it, right now!
Houdini vs Materials and Particles
None. In my opinion, focus on animation, colours, values and design fundamentals. Even though your goal is environment effects, having a strong base of fundamental artistic knowledge will help a lot. Software and technology change all the time. Most materials you’ll use will be simple as bricks anyway. Particle systems are piss easy to understand and use. Scripting is simple and intuitive. Simulations are very straightfoward and a lot of times even done with presets.
The artistic knowledge, practice, observation and mileage will stick with you through any generation of technology.
With that being said, they are obviously important. Any DCC that lets you do what you want to do is good. Be it Blender, Houdini or even shudders Maya/Max. They’re just software 
Pick an engine and stick to it at the start. Remember you’re making games, and you may have to implement effects. The game engine is your bread and butter, everything pours into it in the end so you should familiarize yourself and get as comfortable as you can.
Feel like doing a cool destruction sim? Cool! Now optimize it and put it in the game engine.
Got an optimized destruction sim? Cool! Now make it pretty and work with the rest of the elements you got going in the level.
Now, what do you want to do? We don’t know. You don’t know. Tell us specifically what you want to make and we can point out ways to do that thing. As you practice and make more things, these thing will add up and start forming bridges and connections in your brain and you’ll be able to come up with cool stuff on your own!
Do you think you’re more technical and want to go in that direction?
Start studying shaders, shader math and programming. Apply it in your effects and try something new or study something.
Do you think you want to do more simulations and procedural modeling and tool creation?
Then do it, learn houdini apply it into your effects and workflow IN ENGINE.
Do you think you’re artistic and math scares you?
Then get simple shaders going and spend your days animating and playing around with particles and get some crispy timings and pretty eyecandy visuals.
Just keep doing things and you’ll be fine. And things obviously don’t have to be that rigid. I’m just trying to simplify things for you. You should make your own decisions on what you want to do.
Here’s a simple roadmap for you, though imo you should just do whatever you enjoy.
- DCCs
- Game Engine
- Shaders/Materials
– Understand UVs and UV math.
- Particle System
– Understand how to manipulate basic parameters
– Mix them together with Shaders
- Simple Scripting
It’s great that you have a specific direction in mind, though. I’ll suggest finding effects you like in games and start to recreate them in your engine of choice. When you get stuck, research and ask around for help! as @EdwardLouis said, small and manageable projects/studies will carry you very far. Get on it!
Check out Andreas Glad’s Houdini UE4 course on Pluralsight, check out VFXapprentice by Jason Keyser if you’re looking for useful and good premium courses.
I’ll stop rambling and regurgitating. Good luck! (And read the forums!)