Welcome to the forum!
Awefull deal, but I'll take it off your hands for $450.00.
You have done well if you get what you need to put the equipment into operation. The Dillon Square Deal B uses special dies and will not work with your Lee or RCBS dies. The SDB is for pistol only. You will need caliber conversion kit to change to a different caliber ($85.95 which includes: Dies, Shellplate, Powder Funnel, Locator Buttons). Add another caliber, then will cost another $85.95. More information here:
If you shoot a significant volume in one or two pistol calibers, then you'll find the Square Deal to be a good deal.
You can learn the process on the old RCBS press to make sure you want to reload. Try that before investing in the Dillon SDB caliber changeover parts
I'll second the recommendation of reading The ABCs of Reloading book as a good place to start.