You already have a good idea. However depending on how old the machine is you might need to put the /boot partition at the beginning of the drive. Which will only need to be about 20Mb, depending how many kernels you want to try. I have mine set at 128Mb, just so I have space for test kernels.
I would not bother with LVMs. These are useful if you have two or more drives and want to make it look like one big drive.