Help Best gun to CBT (in the southern USA)?

[Campanella]

I'm in the USA for now, I have citizenship (dually between it and Germany), should be able to purchase a gun fine. If state specific laws are important, I'll be an Alabama resident soon, but right now I have residency in Texas. I can hold onto my Texas residency for longer if I'd have better chances with it than Alabama for something; but I figure both locations would provide the most free choices in the world. Would prefer something under $400, inexpensive options would be great, but of course I prioritize something that kills instead of disfiguring me and can go higher if needed.
I'm sure there's already been discussion on this, maybe there's something I can be linked to? I'm worried since I always hear mixed opinions on what type of gun (I've heard "Consider using a shotgun first!" and "Absolutely do not use a shotgun." said on this forum, never with further information as to why) much less any specific models. I don't know the first thing about guns so I would like to learn in-depth what I'd need to know and more. It'd be nice to get a real discussion over this with the pros and cons of the different options clarified for once. Failing is my biggest fear. I personally just want something that's nearly certain to kill me as I'm sure others will too.
I've never gone out on my own, so directing me to shops I can make online orders with and just go pick-up from or however it all works would be appreciated here. My only personal input is that I'd prefer SN, I'm too likely to chicken away from any gun as I already have before, but I'm not sure if I'll ever be able to find sources for it (I'm open to help for that too but I'm not sure if I can even recieve or send DMs on here yet, hahah...) so firearm it is.
Posted this in the wrong section at first and want to make sure any eyes that could help or may appreciate the advice of the former can see it, sorry for the repost!

 

[bananamatcha]

Have you read the firearms mega thread? It's extremely comprehensive.

 

[Campanella]

Have you read the firearms mega thread? It's extremely comprehensive.

Yes, it's part of why I ask for more. It's part of the "use a shotgun" camp, but I've also heard many say a shotgun is unreliable and you need to go with an assault rifle or whatnot. It doesn't give much information about the kind of gun beyond the obvious advice to not use a revolver/handgun if possible followed by a cheap shotgun recommendation.
I do need to read through more of the replies though, I just know from what I've seen it hasn't given me an answer I could place much faith in yet. I believe you if there's something in some of the replies I glossed over or didn't get to so far, it's just difficult for me to take in when most of the information is unrelated to this specific need or chooses around what is least expensive/available in specific limited locations instead of what's simply most reliable out of all. I don't mean to be difficult, I'm only terribly afraid about failure and would spend big or move to either place if I can optimise my chances.