Action cameras (such a GoPro) are horrible when used as dash cams because they're not meant to be used that way. The most annoying aspect of which is you have to start and stop recording each time, and trust me, eventually you're not going to bother, and that defeats the purpose of having a dash cam. They are also not meant to be constantly hooked up to a power source, so chances are, you'd gonna have to rig that up yourself. And lastly, constant recording will mean the camera runs hot, and a GoPro battery is not going to like that.
As far as dash cams are concerned, they are available from $50 all the way up to $500+. You need to think about how much you want to spend, and what kind of features you want. Some of the more basic questions are:
- single, dual, or multi channel? (ie. how many cameras do you want?)
- battery vs capacitor as power source
- do you want an always on parking mode?
I personally prefer capacitor-based dash cams over battery powered ones since they are less likely to fail. Dash cams get quite hot when they are running, and they're subjected to some very harsh temperatures (both hot and cold) when the car is parked. Extreme temperatures tend to kill batteries faster, so capacitor-based cams are preferred. My first dash cam is battery powered, and while it still records, I suspect the battery is kind of dead after 2+ years of usage since it does funky stuff on power up and shut down.
For the SD card, 32 - 128 GB are most common. On mine with a 1296p video, even a 32GB card is good for around 4 hours of footage. But double check that your dashcam supports the capacity you plan on buying. A lot dashcams, esp the older models, can only handle up to 64GB. If you drive a lot, you might also want to purchase an endurance version of the SD card instead of the common, regular ones that is more easily available. The endurance versions can handle more re-writes, so your SD card wouldn't die out as frequently, but they are ~2x more expensive.
May I ask why you are considering a "removable" dashcam, instead of one that is permanently mounted using 3M adhesive tape? The removable ones are typically mounted using suction cups, and the assembly (suction cup + mounting arm) tend to be larger and more visible. Many of the permanently mounted ones are quite small and discrete, and I'd recommend you going that route instead.
Lastly, I'd highly recommend these guys if you are looking for a vendor:
https://www.blackboxmycar.com/
I've purchased multiple dashcams from them, and their service & products have been excellent. Instead of my broad and generalized comments, they'd be able to make product-specific recommendations for you.