I just started reloading for AR-15 and 700 SPS Tactical. This is my first venture into handloading for rifles, so I don't have the experience some the guys have but here is my routine:
• Clean brass (I use different brands for the AR and bolt gun, to avoid possible confusion)
• Size (full length for AR, neck only for bolt)
• Trim (and all the associated work)
• Clean again
Then primer, charge powder and seat bulllet as desired.
To answer the OP's question about what kind of press, so far, I'm just using my single stage to do the work, and it's just fine. I have an RCBS Chargemaster to weigh charges, so things move smoothly with "only" a single stage.
The only reason I'd use my progressive (Hornady LNL AP) would be to produce lots of plinking ammo for the AR-15. Even with a progressive, you still need to address the case prep issues–it's not like loading for pistol calibers.