Definitely osta first and epi second. The Osta will get your joints lubed up nice and will make the epi run easier on the joints. Plenty of people have joint pain on epi. When you bridge into the epi, continue taking 5mg of osta per day for your joints on cycle. I am doing that on my current run and my joints are happier on cycle.
I'd also be careful not to do too long of an osta run beforehand. If you do 8 weeks osta followed by 6 weeks of epi, that is 14 weeks of supression. You had better make sure your PCT is on point.
Here is my suggestion: Osta for 5 weeks at 20mg or whatever dose you desire. The 6th week of Osta would be the first week of the Epi, so Osta would drop down to 10mg and Epi would be whatever dose you desire. The Epi will not do anything in the 1st week but you will still make some nice gains on 10mg of Osta. By the second week of your Epi run, you will drop the Osta down to 5mg going forward and will dose the Epi at whatever you wish for the duration of your cycle. The dosage will depend on your experience. Here is a sample of what I mean....
Osta - 20/20/20/20/20/ 10/ 5 / 5 / 5 / 5 / 5
Epi - 0 / 0 / 0 / 0 / 0 / 30/30/40/40/40/40
I have been running 5mg of Osta on my current cycle (I ran it for 30 days prior to cycle as well) and I am repping out 245 lbs. (10x) on incline bench with no shoulder issues. I would never have expected to be able to do this without my shoulders screaming at me. This is a PR for me on incline bench.