[ubuntu] Help with virtualbox settings

I'm a complete Linux newbie and I've got a couple of questions about properly configuring Ubuntu 13.04 to run on my computer using Virtualbox.

1) How much Base Memory should I allocate to this virtual machine? The default amount assigned in Virtualbox is 512MB and I've tried to run Ubuntu using this setting and it's clearly not enough as the system runs really slow. I've then increased the number up to 1024MB and it seems to be running better. Can anybody recommend anything else?
The host computer I'm running this all on is an HP EliteBook 8460P laptop with 4GB of installed Physical Memory and and 4GB of Available Virtual Memory..

2) What is the ideal size of the hard drive? Again, the recommended size in Virtualbox for the *.vdi file is 8GB. I've tried this setting but it seems to be too small. By the time I've finished installing the OS and applying all the required software updates, the *.vdi file is already up to 7.7GB.
I also tried creating a hard drive of 10GB but I'm wondering if I just should go even larger than that. The host computer I'm running this on currently has 215GB of free hard drive space.
Also, I'm thinking it might just be better to configure this hard drive as Dynamically Allocated instead of Fixed?
Any advice would be greatly appreciated.

Any other suggestions as to how I can properly configure all of this would be welcomed.

Thanks.