New to Rekordbox from Djay Pro / Traktor - Lag Issues on older Laptop

After 10 years on Traktor, I've just purchased a DDJ-1000 and I'm very excited to reset my Libraries with the better smart tagging of Rekordbox. But, I installed Rekorbox 6.5 and I'm experiencing massive lag and CPU drain. The visual waveforms are lagging no matter where I put the Buffer size. The CPU is using almost 50%. 

I am still using my workhorse old Macbook Pro '09, souped up with SSD internal HD running OSX 10.11.6. So I assumed this lag-issue was just about my old machine, but I am reading on the forums that people with new Macbook Pros are experiencing similar issues. 

My Question 1: what version of Rekordbox should I be using with this old machine?

Question 2: where do I download legacy Rekordbox versions?

Question 3: Does importing iTunes to Rekordbox collection double-up files? Or is this just a record of where the files live on the HD?

Thank you so much

Brandon