Implementation of a decryption mixnet, and problems with the size of the key
With RSA and ECC you generally don't encrypt the actual message. When signing, you sign a hash of the message; and when encrypting you encrypt a symmetric-key that can be used to decrypt the message. The message itself is encrypted using either a block cipher, or a stream cipher, depending on what was chosen in the design. As such, with a block cipher, once the message is padded once it's already as long as it's gonna get, and with a stream cipher no padding is needed at all.
Also, it should be noted that ECC-based public-key algorithms operate a lot more like a block cipher than RSA does. With RSA you would need padding at every layer, but with ECC you only need to pad once.