The lenses would indeed leave the corners of the image black (see an example here
). If there is no possibility of upgrading your lenses right away (the A99 is not cheap), keep in mind you could always resort to cropping your images to get rid of the black areas. Another option would be to invest in a prime lens, like a 50mm f/1.4 (which I believe any photographer should have anyway), and gradually build up your gear from there (or just stick with the fifty
If you're looking to take the plunge all at one, and splurge on a FF camera and a set of FF lenses to go with it, be prepared to make quite an investment.