I have 12 years TIS with the Army Reserve. What will my pay status be while at OCS?

You will receive e5 pay at 12 years of service. Upon completion you will be paid at O1 pay at 12 years. You only get O1E if you have 4 years of ACTIVE service prior to commission. Hope that helps!

In the guard and reserve it's all about the points. I dont recall how many exactly, but I got O1E with my points (18 yrs). When you start the OCS prep program (if the reserves have one) you will be paid as an E5. When you begin Phase 1 of OCS you will be promoted (on paper) to E6.

OK, let me try to do this without confusing the hell out of you. Candidates get paid at E5's in the Army Reserve or Regular Army, E6 in the Army National Guard. You will get paid that rate at your 12 years TIS. O1E requires 4 years and 1 day of Active Army or 1460 retirement points in the Army Reserve or Army National Guard as a Warrant or Enlisted to qualify. With Initial Entry Training, your 8 months mobilized, and whatever extra schools you have done, you should be close to that number.
Even if you don't get O1E, you would max out the pay in the first three Officer Ranks by the time you hit each of them.
Now the downside. You have over ten years enlisted, so you will need a waiver to attend OCS. I don't have a clue how easy that is anymore. Additionally, you will have to serve over 10 years as an Officer to retire at that rank. If you got out at twenty, you would end up with the retirement based on your top three enlisted years.