AspNetCore.Identity Custom implementation with MongoDb and claims

Question

I want to use AspNetCore.Identity for my backend. I am using MongoDb, so I am creating a custom UserStore implementation. It is my first time setting this up and I am a little uncertain about the following aspects:

1. Claims without roles: Can I skip everything about roles (e.g., no RoleManager, no implementation of Role related interfaces in the UserStore)?
2. Registering: Am I missing any interfaces which I would need to add to my IdentityBuilder? I did not find clear explanation which aspects I need for my case as a lot of examples were either too simplistic or extremely complex.
3. Claims for auth: Am I setting up the usage of claims for authorization correctly?

This is how I plan setup all identity related aspects:

    public static IdentityBuilder AddIdentityStore
    (this IServiceCollection services, Action<IdentityOptions> setupIdentityAction)
    {
        var builder = services.AddIdentityCore<MyUser>()
            .AddUserStore<MyUserStore>()
            .AddUserManager<UserManager<MyUser>>()
            .AddDefaultTokenProviders();

        var sp = services.BuildServiceProvider();
        var db = sp.GetService<IDatabase>();

        if (db == null)
        {
            throw new ArgumentNullException(nameof(db), "Database not available as service");
        }

        var userCollection = db.GetCollection<MyUser>(nameof(MyUser));
        services.AddSingleton(s => userCollection);
        services.AddTransient<IUserStore<MyUser>>(s => new MyUserStore(userCollection));

        return builder;
    }

And this is how I then plan to use the claims on the user for authentication

builder.Services.AddAuthorization(options =>
{
    options.AddPolicy("HasAbc", policy => policy.RequireClaim("Abc"));
});

Thanks for your help!