Romantic tension is one of those things that's often better managed during revisions, because it's all about pacing.
Craft your HEA to fit your characters. Let them surprise you with the innovative solution they all come up with.
Characters take an approach of "How can we make this work for all of us?" rather than "It's too bad I have to choose one of you."
You are totally permitted to just do the fun parts of this and skip the parts you dislike. Hobbies are for enjoying.
Don't try to tell an "authentic" story. Instead, tell an "inauthentic" truth.
Let somebody else write only allistic characters. You can write a character who is probably, or maybe, on the spectrum, but this does not need a huge reveal or internal struggle—it can just be a thing you do, among other things you do, as an author.
In first-person POV, it's challenging to convey who's speaking without a clunky or clichéd paragraph of self-description.
Adding or subtracting a character in the middle of creating a lengthy work is nearly as challenging as breaking up with a longtime life-entangled partner.
Draw on the best of the way the world is and has been, as well as your most optimistic hopes for what it could be. The real world is very unfair to those on the margins. Use your writing to make up for it.
You're operating by improv theater rules, where as soon as a character introduces a new idea, you say "yes, and" to it. But this theater troupe answers to your direction.