The only thing i worry about is that my mac came with yosemite pre installed.
Then don't roll back to Mavericks..... as Mavericks may not come with the drivers etc for the newer hardware in your MBP....
Use an external drive to boot to Mavericks from.. to test stability of your hardware under Mavericks..
http://www.macworld.com/article/2056561/how-to-make-a-bootable-mavericks-install -drive.html
Once you are happy with the stability of Mavericks and your Mac.. then install Logic Pro X to the external HD too and test with any drivers you use for your own external Hardware....
Then and only then, if all goes well, should you install Mavericks on your internal drive....
Note: You cannot download Mavericks legally from anywhere.. so unless you have made your own copy of the Mavericks installer at some point in the past, you will not be able to install Mavericks legally, from scratch.
If you try and use a backup made from a different Mac.. then again, that backup may not have the correct drivers etc.. for your newer hardware.....
Otherwise, how you install Mavericks, is up to you.. I cannot offer advice on any other methods to achieve this.
Cheers..
Nigel