Is there a maximum number of Enum items?

Yes, the maximum number is 100. If you try to compile this class:

public Enum Demo
{
    A001, A002, A003, A004, A005, A006, A007, A008, A009, A010,
    A011, A012, A013, A014, A015, A016, A017, A018, A019, A020,
    A021, A022, A023, A024, A025, A026, A027, A028, A029, A030,
    A031, A032, A033, A034, A035, A036, A037, A038, A039, A040,
    A041, A042, A043, A044, A045, A046, A047, A048, A049, A050,
    A051, A052, A053, A054, A055, A056, A057, A058, A059, A060,
    A061, A062, A063, A064, A065, A066, A067, A068, A069, A070,
    A071, A072, A073, A074, A075, A076, A077, A078, A079, A080,
    A081, A082, A083, A084, A085, A086, A087, A088, A089, A090,
    A091, A092, A093, A094, A095, A096, A097, A098, A099, A100,
    A101
}

You will get this error:

Maximum number of enum items exceeded: 100