Is there a fix for the Bluetooth issues in OS X 10.10?
If you boot into safe mode, does the erratic behavior persist? (i.e. use the Mac in that mode for hours if possible as opposed to using it to rebuild some system caches and then reboot back into normal boot state)
If you make a new user account, does the erratic behavior persist?
Can you reproduce the keyboard issues in recovery HD and/or single user mode?


Those are the first things I'd test to see if a workaround is possible. Also, get a sudo sysdiagnose every time the OS is laggy - those logs will help if you need to open a bug report with Apple. I've not heard of (nor experienced first hand) problems, but it's also soon in the release cycle.