Is this wrapper around AesManaged ok?

I need to encrypt/decrypt some strings. I've build my wrapper class according to the msdn documentation but with some changes.

Since I want to encrypt/decrypt data with a given string/passphrase, I don't use AesManaged for creating a key. (The user should be able to encrypt/decrypt with a key he enters, and therefore I cannot use the key from AesManaged and I cannot save the key).

I instead create the key by using Rfc2898DeriveBytes (PBKDF2) with a given salt. The given salt is used since I do not store the key and I think because of this, the salt must be always the same.

I then create an IV, encrypt the given string and concatenate the IV and the encrypted string. This will then eventually got saved in a file. This means the IV gets save together with the encrypted data.

Questions:

1. Is it ok to store the IV together with the encrypted data?
2. Is there another way to create the key without using the same salt everytime(Based on a given passphrase)?
3. Is this encryption done using AES128 or AES256?
4. Will the IV be always 16 bytes, or can this change?

    static void Main(string[] args)
    {
        const string stringToEncrypt = "String to be encrypted/decrypted. Encryption is done via AesManaged";
        const string password = "m1Sup3rS3cre!Password";

        string encrypted = EncryptString(stringToEncrypt, password);
        string roundtrip = DecryptStringFromBytes_Aes(encrypted, password);

        Console.WriteLine("Original:   {0}", stringToEncrypt);
        Console.WriteLine("Round Trip: {0}", roundtrip);

        Console.ReadLine();
    }

    static string EncryptString(string plainText, string password)
    {
        string encryptedString;

        using (AesManaged aesAlg = new AesManaged())
        {
            aesAlg.Key = PasswordAsByte(password);
            ICryptoTransform encryptor = aesAlg.CreateEncryptor(aesAlg.Key, aesAlg.IV);

            using (MemoryStream msEncrypt = new MemoryStream())
            {
                using (CryptoStream csEncrypt = new CryptoStream(msEncrypt, encryptor, CryptoStreamMode.Write))
                {
                    using (StreamWriter swEncrypt = new StreamWriter(csEncrypt))
                    {
                        swEncrypt.Write(plainText);
                    }
                    var encrypted = msEncrypt.ToArray();

                    encryptedString = Encoding.Default.GetString(aesAlg.IV);
                    encryptedString += Encoding.Default.GetString(encrypted);
                }
            }
        }
        return encryptedString;
    }

    static string DecryptStringFromBytes_Aes(string cipherText, string password)
    {
        using (AesManaged aesAlg = new AesManaged())
        {
            aesAlg.Key = PasswordAsByte(password);

            aesAlg.IV = Encoding.Default.GetBytes(cipherText).Take(16).ToArray();

            ICryptoTransform decryptor = aesAlg.CreateDecryptor(aesAlg.Key, aesAlg.IV);

            var encryptedByteArray = Encoding.Default.GetBytes(cipherText).Skip(16).ToArray();

            using (MemoryStream msDecrypt = new MemoryStream(encryptedByteArray))
            {
                using (CryptoStream csDecrypt = new CryptoStream(msDecrypt, decryptor, CryptoStreamMode.Read))
                {
                    using (StreamReader srDecrypt = new StreamReader(csDecrypt))
                    {
                        return srDecrypt.ReadToEnd();
                    }
                }
            }
        }
    }

    private static byte[] PasswordAsByte(string password)
    {
        byte[] salt = Encoding.Default.GetBytes("foobar42");
        Rfc2898DeriveBytes passwordBytes = new Rfc2898DeriveBytes(password, salt);

        return passwordBytes.GetBytes(32);
    }