Writing a fictional ethnic minority

Dealing with race is scary for a lot of people, because of what I'm calling the "vacuous critics" problem.  There are so many people saying terrible things about race, that people are afraid of opening the doors to those people, or worse, being that person.  But I'm not sure that this fear serves us well in "post-racial" US, where most people of my generation refuse to acknowledge that racial issues still exist.  In particular, it doesn't serve people well when they try to write fiction.

There's the easy way of including ethnic minorities in fiction, which is to mention or imply a character's ethnicity, and not make anything out of it.  And then there's the hard way: dealing with a character's ethnicity with the nuance that the issue deserves.

In my novel, I take the easy way with several characters.  But then I also take the hard way, inventing an entire ethnic minority, which includes two main characters.  It's a way of talking about race, without talking about any race in particular.

Now, I'm not exactly coming from experience here, since it's my first novel and I've written like 10% of it.  But it seems to me the first step to creating a nuanced ethnic group is to write out their history.  I decided that there were maybe three qualitatively different ethnic histories (in the US--there might be even more outside the US).

1. There are Native Americans, who lived here before Europeans moved in.
2. There are African Americans, who were imported as part of the slave trade.
3. There are immigrant groups.  Some of these groups (eg Irish, Italian) eventually got conglomerated into "white", while others groups probably never will, because they're not light-skinned, or otherwise look different.

I thought it would be easiest to write an immigrant group, since the others might require more radical alternate histories, and I'm not feeling quite so adventurous.  Furthermore, the first two histories would read as thinly veiled metaphors for Native Americans and African Americans, so it almost seems like you should just be writing about the real deal.  Lastly, I'm more familiar with immigrant issues, being half Asian.

I guess I just inadvertently invented an Asian American subgroup based on my own experiences!  Oh well.  It's basically impossible to write something that would generalize to all ethnic groups, even just to groups within the US.

The issues of the ethnic group don't have to be complicated.  Here's a really basic and ubiquitous issue for immigrants: First generation vs later generations.  Bam.  Here's another one: stereotypes.  Another: feeling distant from, and inferior to white people.  Easy.  At least in theory.

And then there are more difficult issues.  For instance, I'm inventing a religion.  But most of the characters are not part of this religion, they're Catholic because they were converted by colonists.  Colonialism is super complicated.  Luckily, in a work of fiction I don't need to deal with it explicitly, I just want it in the background to the story's events and dialogue.