Stonehorn

Keep in mind, that you already have a nice set up of lenses. You should only consider extra prime lenses if you need that extra background seperation and low light capability. At the beginning you should use your 18-55 for portraits. It's a georgous underated piece of a kit lens. Even at F4 you'll have a nice background seperation.
 
23mm F1.4?!
Nope, you have the 10-24 already. Or do you need that extra low light capability?!
 
56 F1.2?!
Nope, it's a portrait lens and not that versatile any more. Expensive as hell as well. You should only buy it if you are really into portraits or you have money to spend. And you mentioned that you have a nice Nikon set up for that kind of work already.
 
35 F1.4/F2
This would be my first prime lens suggestion for you. 35mm is still versatile and very nice for close up portrait work. The difference between F1.4 and F2.0 isn't that much. F1.4 has only a bit more blurry background. I wouldn't buy the old one anymore. I actually sold mine for the new one. The new one is a perfect fit for myX-T1. The AF is defintily faster, it's dead silent, at F2.0 it's as sharp as the F1.4 and it's smaller, cheaper and WR as well.

I've been to Norway and Sweden this summer and it was raining a lot. And I mean a lot!!!
I bought some WR lenses after the trip because I wasn't able to take a lot of pictures due to the heavy rain. All my friends and family thought I had sunny weather all the time. But I basically took all the shots during the narrow dry windows.
It would have been nice to have some shots representing the real soaked wet feeling I had nearly all the time.
 
I'm happy that you like your new toy I'm impressed by this little fella as well. I sold my 23mm F1.4 and picked up a 16mm F1.4 WR. So next time in Norway I'll have no excuse anymore.
I don't miss the 23mm range on my X-T1 at all. But I do own the X100t as well so the range is still covered.

Keep in mind, that you already have a nice set up of lenses. You should only consider extra prime lenses if you need that extra background seperation and low light capability. At the beginning you should use your 18-55 for portraits. It's a georgous underated piece of a kit lens. Even at F4 you'll have a nice background seperation.
 
23mm F1.4?!
Nope, you have the 10-24 already. Or do you need that extra low light capability?!
 
56 F1.2?!
Nope, it's a portrait lens and not that versatile any more. Expensive as hell as well. You should only buy it if you are really into portraits or you have money to spend. And you mentioned that you have a nice Nikon set up for that kind of work already.
 
35 F1.4/F2
This would be my first prime lens suggestion for you. 35mm is still versatile and very nice for close up portrait work. The difference between F1.4 and F2.0 isn't that much. F1.4 has only a bit more blurry background. I wouldn't buy the old one anymore. I actually sold mine for the new one. The new one is a perfect fit for myX-T1. The AF is defintily faster, it's dead silent, at F2.0 it's as sharp as the F1.4 and it's smaller, cheaper and WR as well.