Thank you for the suggestions!
My thoughts on these builds:
SC Assassin is something that in theory sounds good, but at the same time feels like it could benefit from some extra stuff other classes might have. If the SC is powerful and fun keeping to the theme of using guns AND is also useful in a party fight - I don't really want to leave my party behind to do stuff like hit, run back, stealth, wait, go strike again and repeat. I want to engage fights with everybody and use team synergy for fun and profit. I don't exclude the occasional cheeky one shot and I do want that BIG opening burst damage, I just don't want that to be the only thing my rogue can do. He should be able to handle himself during a fight in the backline.
Assassin/Helwalker: Don't really understand the synergy here. My understanding is that monks want to take damage to build up their resources, but I really don't want my rogue getting hit right? Also, aren't most of their abilities melee?
Assassin/Bleakwalker: I was checking the skills and it does sound spicy! I guess mostly for the sworn enemy, flames of devotion and auras as the rest isn't very relevant for the rogue.
Assassin/Devoted: Looking at the fighter skills and the devoted passives, honestly this looks quite amazing. The multiple "Barrage"s and the penetrating strike alone makes this very appealing.
Assassin/Ranger: I like some of the skills rangers get as well as the passive from sharpshooter. I don't really like the pet as they tend to die instantly and getting that debuff makes me not really want to play with a ranger at all. I can understand the suggestion for Ghost Heart (that would be my pick as well given this pet issue) but having a subclass that simply removes the hindrance of the pet just feels like there's a problem with the class in the first place.
Assassin/Chanter: This makes me think of bards Don't really like the class combination.
Trickster/Martial: Sounds like an awesome combination, but for a future playthrough where I would most likely go melee.
Assassin/Cipher: I still feel kind of weird about the Cipher class, even in PoE1. I think I would rather have my other companions work on debuffing the enemies.
With all this, I'm kinda undecided between SC Assassin vs Assassin/Devoted. I like the assassin subclass, the Devoted bonuses and I don't really think I'll have an issue with the Devoted downside as I was really planning on taking pretty much only Rifle and pistols. What would be your opinions regarding these two options? How much do I lose out in terms of Rogueish power and tricks by going MC? How much power would I lose from the MC synergies by going SC? I'm not particularly interested in just having the most finely tuned and powerful late game character, I want the character to be fun and a positive contribution to the team throughout the entire game.