Im playing a Wastelander/Scavenger type character that only cares about himself, Cait and my community at Abernathy Farm. I'm pretty far in the game but haven't joined any factions. Haven't talked to Nick yet but I experienced my wifes death again at the Dream place with Irma. so I was wondering if its game breaking if I disabled essential characters and Killed Preston and his group at Concord, I don't like their begging or nagging me to help and I don't support the Minutemen. Can I complete the game without joining any factions? My character hates Synths, hates the institute as well as the BOS and probably wouldn't even like the Railroad but I could work with them but I wouldn't want to join them. Synth Sympathizers aren't my thing.

Is it possible for me to reach the end of the story with no factions? and Will it break my game if I kill Preston and crew?

Sorry, I don't think so.

The one main issue I have with this game is how almost impossible it is to play evil. In RPGs I always want to maximise my character's evil, i.e. murder as many innocents as possible, [censored], steal, join the most evil factions (slavers, f.ex.) and so on. It's fun. But in F4, if you happen to steal a cigarette pack (while hidden and undetected); the whole settlement will start shooting at you and you will be unable to complete any missions with that faction. In F3, you could steal all you want, as long as you weren't caught. Not so in F4, which is very annoying.

Also, not joining the Minutemen will result in you not getting the best workshop, which is The Castle. And I am not even sure if it's possible to not join them. I [censored] hate the Minutemen. Their quests are repetitive (same [censored] 2-3 farms asking me to save some kidnapped idiot, kill some raiders, kill some ghouls or kill some super mutants over and over and over again) and the rewards beyond [censored] (50-150 caps for saving their lives). I hate it when the game feeds me grinding quests without me asking for it. It's fine to have such quests if one wants to just kill something when bored, but one should be able to choose when to get those quests.

I don't want to be evil per say but I see where you are coming from and I agree. I would just like to complete the main story independently from any factions. None of them pique my interest and I already told Preston to [censored] off and he was pretty upset, I just wanna turn essential off and shoot him now, don't really care about the castle. Abernathy farm is my favourite

As far as I'm aware you can't complete the main quest without support from a faction. To be fair, it's presented that doing the stuff you do in the main quest is difficult even for the well equipped and organised factions there are, let alone doing it on your own. What I'd personally do in your case would be to join the Minutemen, put up with Preston until you've finished the questline (using your Farm as your main base), then banish him to a settlement all on his own in some corner of the map so you never have to deal with him again. You get your own faction to do what you want with, you can build up as many or few settlements as you like too.

Alright I will probably do it that way, but I am killing Preston in the end. No banishment, just death.

Actually, is it possible to just side with the railroad and never deal with preston at all or is he essential to the main plot as well as the minutemen?

I believe you can completely ignore the Minutemen and just team up with the Railroad.