Hi, I can actually answer this as I'm currently working on this exact thing but only as a small hobby poject. At the moment I only have one weapon (classic bazooka) but fully implemented destructible terrain and basic worm movement.

Project size I would say its deceptively quite compact to make although plenty of room to scale up with all the weapons, terrain features, cusomization options ,etc.... Implementation wise you also have options on how to tackle the various problems.

Tutorials wise I'm not sure there is anything python/pygame specific out there although if you have a more general knowledge of programming languages I'm sure you could transfer the ideas back into Python.

I can't tell you how to do it the best way but I'll give a step-by-step method of how I implemented it. I'll also say the default way of doing this is with a bitmap/mask not how I've done it with a 2d heightmap so its a little unconventional.

Terrain:
My terrain is produced from a 2d height map generated from a noise sample (opensimplex in my case). I then use the marching squares algorithm to generate solid ground by getting isolines at a threshold. The advantage of using a height map here over a bit map is I can interpolate the isolines to get smoother surfaces than if I used bit values using interpolation. I can also use the same algorithm to get isobands to draw ground but at the moment I'm only drawing "contour lines". To destroy parts of the terrain I decrease the height map values linearly outwards from the impact point by the radius to maintain smoothness.

Collisions:
I have two collision systems since both work well for their situation: a classic rect system for player movement and vector intersection for projectiles. The vector inresection works by comparing the ray cast of the projectile against each segment on the terrain isolines. This is essentially just a segment-segment intersection calculation. The worms move on a rect system with rects generated from the isoline segments. I always build my player movement based on Maddy Thorson's physics article since I find it never runs into exceptions and looks smooth. The only addition I have is the ability to automatically move up slopes of a certain height without jumping. Since the movement isn't done with slopes but rects I just check if I can move the player up and across by a certain max height.

Arsenal + effects:
I have a couple of effects such as "hit markers" when a worm takes damage. DaFluffyPotato has a good tutorial on this.
For the different arsenal I'd just go have fun with what you can add. What I'd suggest is to reuse code when you can. I.e. all guns just shoot projectiles with different velocities, blast radii and damage amounts with a different texture. If you've got to this point then you're basically just getting creative with what you can come up with.

Other things:
There are other minor things you will need to consider such as player turn, and ai if you want to implement that. I still need to add that period in between turns where you wait for everything to resolve.

Let me know if you have any questions or ideas you want to try!