Hi Clare and welcome to Seasoned Advice!
Some fermentations start quickly, whilst others take a little longer. It varies depending on what you're fermenting, and when and where you're fermenting it. This is part of the reason salt is used in fermentation. The salt helps keep various salt-intolerant organisms at bay until the salt-tolerant lactobacteria can take over and become the dominate organism in the environment.
The lactobacteria release carbon dioxide gas as they digest the sugars in the food. Then they ahem fart out bubbles of CO2, which creates a blanket of heavier than air, gas on the surface of the ferment. This is what displaces and forces the air / oxygen out of the airlock and it's also the reason why people shouldn't constantly be opening the lid / airlock and stirring their ferments.
An active ferment can mean that the brine makes its way into and out of the airlock. In such cases you should remove the airlock, and cover the ferment as you resterilise and refill the airlock. Clostridium botulinum can also create gas as it grows, but whether it creates enough gas to make sauerkraut overflow in just three days is kind of beside the point.
The real issue here is that no one can give you a definitive answer to whether the overflow was caused by fermentation or something else. Given the time frame involved and the ingredients used, I would go as far as saying that it sounds like fermentation is the likely suspect (I've had the same happen a few times in the past) but the only way you'll get an informed, reliable answer is to test the pH of your fermentation. At the very least, you could use some litmus test paper specifically for low pH but the colour of what is being tested can make test strips unreliable.
I'd say you're far better off getting a cheap electronic pH tester, which can be had for less than $10, and assuming you verify their accuracy, should give you a reliable way of telling whether your ferments are safe. Cheap pH testers often have limited lifespans though, as their non-replacable bulbs can get old or dry out. So personally, I opted for a more expensive but much longer lasting and more accurate Apera PH60, which can have its bulb replaced.
After two weeks it’s still red. Does that indicate that it’s acidic
enough to prevent Clostridium botulinum growth?
It could indicate that it's acidic but again, it doesn't guarantee that it is acidic, or acidic enough to be safe.
Initially I wasn’t getting enough juice from the raw cabbage so I
added salt water.
On the subject of salt... always make sure you calculate and measure your salt percentage properly. As I said at the start of the post, salt is there for more than just taste but a lot of new fermenters just eyeball quantities or they use unreliable, volumetric measurements. You should also try to use salt that is free of any additives such as anti-caking agents as they can inhibit fermentation.
For flavoring I used juniper berries, black pepper, cardamom, garlic powder, a little home-made habanero pepper sauce, and a little bit of pickle juice for the dill flavor. I don’t know if the acidity of the pickle juice affected fermentation.
The recipe sounds nice! Without knowing the quantity and acidity of the pickle juice though, it's not possible to say whether it inhibited the fermentation in a significant way.
