How resilient to attackers with extreme resources available is this encryption method? How could the following scheme be made more resilient to attacks capable of utilizing massive amounts of resources?

Assume all random values are cryptographically secure.

Key derivation: scrypt using a random 16 byte nonce. The work factor is 1048576 which takes a GB of memory and ~3 seconds to compute on a 2500k.

Authentication: HMAC with SHA-512 as the hash function. Authentication key is the SHA-512 of the AES key. HMAC checks are done using equal time compare.

Encryption algorithm: AES-256 in CBC mode using a 16 byte random IV.

Asymmetric keys are used in TLS which allows access of the encrypted data over a network.
4096 bit RSA is used due to ease of generation.

The end result of the cipher text can be described like so:

nonce | iv | cipherText| HMAC Digest


Thanks!

EDIT: Sorry guys I should have described my use case. This is for encrypting a specific file.

The authentication is used to securely ensure that the file hasn't been tampered with as well as check the key before decryption.
All looks pretty secure except for your auth key derivation. You should use a better key derivation method like HKDF instead of just SHA-512.

I don't think your random nonce is doing anything in this scenario - an attacker who wants to brute-force a weak password wouldn't be slowed down by a nonce transmitted in the clear. Why not just use a randomly-generated AES key and a key exchange scheme? This would really confound an attacker with massive (e.g. nation-state level) resources. The NSA would laugh at your puny attempts to use scrypt to slow down brute-forcing.

EDIT: Wikipedia's article on Diffie-Hellman key exchange should get you started.