I have always heard that Pathfinder is one of the most customizable/crunchy systems in existence, and that you can make "TRULY ANYTHING" in it, which is cool, but I have nowhere near the proficiency with the system to know how true it is or not, so I want to propose a character and then see if somebody else has the time and talent to offer suggestions on how it could be achieveable. Of course, if it is impossible, that is also good to know, just please remember that I am asking because I really want to play it. I have tried to build it in other syatems and had mixed results at times, but anyway:

THE CONCEPT: I want to get to play a sniper. Now, I know that the Gunsliner already has an archetype for that (or a prestige class? I was very confused when I got that deep into the archive of nethys, honestly.) So, I know it exists in name, but I am meaning even more specifically: someone with incredibly high DPS, stealth, a great big boom boom stick, and the ability to be all the way off of a battlemap or potentially on their own smaller, seperate battlemap far away, just going "pop, pop, dead".

I get that this would not really be achievable from first level, and I am also decently sure that magic would only ever help such a setup, but I don't know enough about the rules of pathfinder and multiclassing and etc. Etc. Etc. to even really begin to figure out how to make such a character.

And just to be clear, before anybody says it, I do not care that longbows are more common in fantasy settings and have ridiculously long range already built in. I don't want the character to have a bow, I want to have a big ole longgun that goes BOOM. I mean no disrespect to all of the fans of archery or the folks who really love the archer options, but yeah, for this specific character, I am thinking of a very specific sort of fictional character.

Think Doc Brown in Back to the Future 3.

Is that possible? How do I make that, rules as written, without upsetting a GM or needing to homebrew a ton of other added nonsense or making them do any extra work about it.