Does GDAX have weekl buy and sell limits? I understand that CoinBase has weekly buy and sell limits. Does GDAX have this as well?
No.

From the GDAX support page (source):


  Deposit (BTC, ETH, LTC): Unlimited
  
  Deposit (ACH or SEPA): Varies
  
  Deposit (USD via wire): Unlimited
  
  Trade: Unlimited
  
  Balance: Unlimited
  
  Withdrawal: $10,000/day for individual accounts and $50,000/day for
  institutional accounts. To be considered for higher withdrawal limits,
  please go to your Settings within GDAX and click "Increase Limits."