What is the minimal size USB 3.0 flash drive that I would need to run Ubuntu. Would it be as fast as running it of the hard drive? Would it have access to all of my laptops facilities? I am thinking of investing in a 64 GB USB 3.0 flash drive to run Ubuntu off rather than bothering with a separate partition> DOES THIS MAKE SENSE?
For a Full install of Ubuntu 12.04, and above, minimum disk space recommended is 5GB.
Ultimate speed depends on the make and model of the flash drive. Some USB3 flash drives are faster than others.
Your solution makes sense to me. Your laptop should see it as just another drive.
Probably a good idea to encrypt the drive and home folder as flash drives can be easily misplaced.
Really there is no minimum or maximum size, it depends what your plans are. A large enough flash drive can be used to save any files or downloads that you might need or do. Keep in mind that the flash drive has to be persistent.
Note: Keep in mind that because of the write cycles that happen, the life of the flash drive may be reduced.
Now as far as the speed issue USB is designed for external and portable use, and is also a high-latency, high-throughput interface. HDD drive is definitely faster than USB pen drive except for access time.