CtA3 essentially comes with all the functionality of CTA2, plus a whole lot more. So all the content currently available for CTA2 can be used in CTA3. The reason there is not a lot of content available right now for CTA3 is not because it is an unfinished product as you enquired, but because it is a brand new product. Reallusion themselves will no doubt bring out a lot of CTA3 content, but in addition, independant developers like myself will have new CTA3 content out in the future. Its just that we have only had the software ourselves for a short time.
With regards to which version you should buy, in my opinion, this is what you should base your decision on-
1) "Do you want to develop your own characters for animation?". If the answer is yes, then CTA3 is the way to go. G3 Character creation is much easier for CTA3 than G2 character creation is for CTA2. But you can still make G2 characters in CTA3 should you wish. So long as you buy the Pipeline version.
2) "Do you like the new flexible bones for character and props". If the answer is yes, then CTA3 is the way to go, because this feature is not in CTA2.
3) "Price". If you only want to start experimenting with animation, youre not sure if its a long term thing for you and you can buy buy CTA2 WAY cheaper, then go CTA2.
Also, if you wanna know anything else or I can help in any way, just email me at email@example.com
and Im happy to help.
Have a great day and good luck with your decision making process.