2000+ payees from years of Quicken for Windows, how to easily delete in MAC 6.3?

You can't get rid of Payees in Quicken Mac, because the database is constructed differently. Every transaction's Payee is in the Payee list; there isn't a separate list of memorized Payees like in Quicken Windows or the older Quicken 2007 for Mac. So if you edit a Payee name in one place, it can be changed everywhere in your database.

Instead of deleting old Payees, you can make Payees hidden. This leaves them in the database, and doesn't affect old transactions, but prevents the Payee from showing up in dropdown menus. To do this, go to Window > Payees & Rules, click on a Payee, and click the "—" icon at the bottom. Unless you have the "Show Hidden" checkbox at the top of the window checked, this will make the Payee immediately disappear from the window.

If you don't see a Hidden column in your Payees window -- the developers hide it by default, I suppose to keep things simple -- just Control-click on any column heading, and then check Hidden to make that column visible. Note that Hidden Payees will not show in the list unless you have the "Show Hidden" checkbox checked.

If you really don't want a Payee around any longer, hidden or otherwise, you can merge it with another. This is useful if you have multiple spellings or variations of what should be a single Payee.