The width and length of the container you have are OK, but a height of about 16-20" would be much better. If you can also get a longer or wider tank that would be OK too.
Have a look here for calculating the volume of water based on the dimensions;
http://www.redearslider.com/calculator.html
As far as a basking area, cork bark would be great and not too expensive. I know several people here have used plumbing pipe to build cheap effective platforms to put the bark or other basking material on.



