In a Quicken file you can have:
Accounts - Up to 512 accounts of each Account Type (spending, credit, investment, etc.);
Transactions, reports, and graphs - As many as allowed by the size of your hard drive;
Categories, subcategories, and tags - Up to 32,768 of each; subcategories can be nested 16 levels deep;
Attachments - As many as allowed by the size of your hard drive;
Trackable stocks - Up to 2,000 total;
Split lines - Approximately 250 total per transaction;
Paycheck Line Items - 30 total line items per paycheck tracked;
Dollar amount - A Quicken file cannot have an entry that is larger than 99,999,999.99. This includes number of positions (shares) as well as amount of dollars.
Note: Once the limit has been reached, there is no way to decrease the limit count. For example, deleting an account will not "free-up" the code-line occupied by that account. This means that you cannot delete list elements and then be able to create new ones. Your only option once the limit is reached is to start a new Quicken file, keeping the current file as a historical copy.