How many addresses can the safe and blocked lists hold? 

According to Microsoft, approximately 2000 total.  If addresses are long, the list will hold fewer addresses; if addresses are short, the list will hold more. 

The total size of all lists combined cannot exceed 512K. Once the 512K limit is reached, Outlook alerts you and additional addresses cannot be saved until you make space by removing some from the list.

Which should be removed from the lists? 

Go to Inbox / Actions / Junk E-mail / Junk E-mail options ... button / Blocked Senders tab

Delete the address without recognizable names, Ex.: xpdklhti@hotmail.com 
Most of these free e-mail accounts are used only once to send spam, and then the account is closed.

Look at your blocked senders list.  It might be wise to change some blocked senders to blocked domains, especially those companies that are easily identified.

Ex.  zwgvtzyz@freebies4you.com  (the system blocks the name of this one sender)

Click edit and delete the senders name. Only keep the domain address @freebies4you.com (the system will block all the messages coming from this company). Adding domain names keeps your lists short, functional, and saves space.

Remember, you never want to add @aol.com   @hotmail.com    @yahoo.com  etc. to your blocked senders' domain list. 
I recommend that you use more of the .com domain lists.

Many spammers are now coming from Russia(.ru), China (.ch), France (.fr)
Ex.: kzpyxz@transmail.com.ru I have added some of these domain names to my blocked senders' list

There is always a safety zone:  Blocked senders are automatically forwarded to the Junk E-mail folder for review.
Open this folder every day to check names and delete the messages.