Crashing and slow down

I should say I normally don't have any issues with this, but one particular project has caused a lot of trouble. Almost not usable now.

My normal camera, normal footage, a few animation codec items from AE, but nothing I haven't used before.

I experienced a crash. Was instructed to save as a different file, and continued working. Over the course of the editing process, this happened 12 times, and each time I have noticed some slow down of the application. Now it can take over 5 seconds after pressing space, for the program to play. It can be extremely laggy, but will stabilize after a while.

What I need to know is:
How can I find out what is causing the crashing. Disk related, computer related, effect related?

What can I do to repair the issue, so that I am not just adding to it with each consecutive save?

What is the CORRECT approach when experiencing a crash? Instead of saving the recovery file and incrementing the filename, should I actually return to one save earlier? and manually increment my saves or use an Auto save?

Thank you.