Congrats!
I wouldn't worry about the thumb drive speed - if that's a "cheap" USB 2 thumb drive, the transfer speed would be limited to 60MB/s, and then there's the flash device in the drive which is probably much slower, could be 10-20MB/s, so I reckon that sounds about right. Likewise with the YouTube buffering, another IO bound limitation.
But yeah, if it came with the OS pre-installed, chances are there's lots of stuff you can remove from the startup and lots of services that can be stopped. I wouldn't expect gaining much outright speed from that tough, mostly freeing up some memory and reducing the boot-up time.
In any case, that computer will haul a$$ for your music apps. Have you gotten around to try some soft synths on it? What are you planning to run?