To expand your knowledge--
Do a search in this forum (use Googe, site focus) on the phrases "Lee Turret" "Classic Cast Turret" and similar phrases--you'll find a lot of info.
To answer your questions--
1. Yes, you need a second turret IF you want to leave the dies installed and setup--and believe me, you do.
2. For the .40 cal die setup, buy the Lee deluxe / 4-die kit. A little over $30.00 on line.
3. For the .223 die setup, "it depends"--I am guessing you are running a .223 semiauto, so do get the full-length sizer and the FCD die.
And to add some other needs and thoughts--
1. If you haven't gotten the Safety Prime with your turret kit, get that--it isn't absolutely necessary, but it does make primer installation much easier once you get the hang of using it.
2. I'm assuming you have a Lee Powder Measure and a Lee Scale--so buy a Double-disk kit for loading the Rifle ammunition, and get an adjustable charge bar if one didn't come with the press. You may want to use the Lee Dipper routines, but you will probably end up wanting to use charges more specific than the Lee Dippers can give--so be sure you have at least the Lee scale.
3. Get a weight-check kit for the scale.
4. For the time being, I am assuming you will start loading .223 in 'single stage' mode, so you shouldn't need a rifle charging die to work with the powder measure. The funnel in the die set and / or in the kit should work OK.
5. Personally, I would recommend getting MAX cart gauges to check your finished rounds. It's true you can use the firearm barrels/chamber, but the MAX cart gauges are MUCH easier for beginning reloaders to use in the workflow.
6. I assume you do have calipers; you will also want some sort of case trimmer-deburring tool (s) for the .223 cartridges. The Lee products (get the ball handle as well) are a good place to start.
7. If you don't have at least one of the 'reloading books,' get the Lee one, and the Lyman book--those should get you started OK. Besides the books, see various powder / bullet manufacturer's online sites for recipes.
Start out with the .40 Short and Weak; straight-walled pistol cases are straightforward to reload for. Learn to set up your .40 loads with a carefully set LOA--the cartridge can be "touchy" and go overpressure quickly if the recipe LOA is shortened--so be sure you learn adjust the FCD properly.
And always ask questions. There is no dumb question when one reloads, ever.
Jim H.