I have a Server with ~16 podman services, each their own user, network namespace and uids. This is managed using NixOS and Home manager (which supports quadlets) but I am changing my setup to a single node k3s cluster with user namespaces because that seems simpler to manage. Here a snippet for how the subuids/subuids are defined:

users.users.<username> = {
        subUidRanges = [{
            startUid = 100000+65536*( config.users.users.<username>.uid - 999);
            count = 65536;
        }];
        subGidRanges = [{
            startGid = 100000+65536*( config.users.users.<username>.uid - 999);
            count = 65536;
        }];
        home = "[...]";
        isNormalUser = true;
        linger = true;
        group = "users";
        openssh.authorizedKeys.keys = config.users.users.root.openssh.authorizedKeys.keys;
    };