PS Vita and PSN: Limit purchasing ability

Solution 1:

Yes, you are 100% correct in your understanding.

To prevent access to the PSN store, you have two options.

1) turn off "auto-login" for PSN. This way anytime you want to purchase/download something you need to provide the password.

2) delete the wi-fi profile off of your Vita after it's activated so it can't connect to the Internet. From there you can manage purchases/content either via the PS3 or Content Manager on your PC. (or temporarily re-add the wi-fi connection as needed)

Pretty straight forward.

Oh, and as others have suggested stay away from sub accounts. They have lots of ugly pitfalls.