Help with a writing "transition"

Hi everyone, I hope this question is allowed! I've been struggling to transition between two types of writing and wonder if anyone has gone through similar or has any tips. I've written a huge amount of fanfic over the space of several years, and while I was never quite a BNF, my fics were reasonably well liked and decently popular. I enjoyed writing them and interacting with the community and met quite a few great people that way. But, there's always a but...

Over the past 2-3 years, I've been dabbling in some non-fandom writing - I have two ideas that would work for a full-length novel, and several ideas for short stories. Although I've done a lot of background research, notetaking and writing the ideas down, I struggle with stop-and-start writing and the shift in approach. In fanfic, I could focus on the character interaction and dramatic irony - the main things that made it fun for me - straight away without having to build all the scaffolding. So that's a bit of a technical issue I could use some help with. The other thing is that unfortunately, you can never be sure if people are reading your fics because of your writing style or because it's their favorite character/ship. That's left me feeling like no one (other than people I know) will be interested in reading my original writing, if it ever gets published at all. And publishing itself ALSO seems like an insurmountable hurdle. I have something of a rejection phobia, which on a good day I can ignore, but on a bad day it makes me think I don't have the right personality for writing as an industry and should just do something else.

TL;DR these are my questions:

How can I kick myself into writing more and obsessing over how hard it is to get published less? I will never write it if I'm constantly thinking about failure, I know, but my brain wants to plan and the uncertainty is hard to cope with.

How can I bridge the gap between very character-focused fanfic and having to build the entire world from scratch? I'm good at editing once I do have something, but I get blocked a lot on getting the first draft out!

Thanks for any advice on either of these, I'd really appreciate it.