I have been in the Army Reserves Nurse Corps for a while now and my only regret is that I should have done it all earlier (smile).
I am presently with the 8th Medical Brigade, 7238th Medical Support Unit out of Fort Hamilton, New York (recently transfered over from Fort Wadsworth, and before that Fort Dix/Picatinny Arsenal 4219th USAH)
Your MOS will be 66H (RN) and with your critical care background you will be given an additional skill identifier (ASI) of 8A
OBLC is Officers Basic Leadership Course and I believe it will be ten weeks long(?). When I went it was only two weeks long, much too short for all that you will need to know and learn, so ten weeks is much better! You will qualify in weapons, LandNav, etc.... Once you take the Oath you should be given the Officers Handbook which will fill you in on all you need to know BEFORE going to OBLC.
One thing to always keep in the back of your mind is....You are a Soldier first, Nurse second.
As for our Battle Assembles (BA, old term Drill Weekends) I guess it is according to where your TPU is or will be. Do you know where your nearest Reserve Unit is located? Will you be IRR (Individual Ready Reserve)? These are questions that your Health Care Recruiter - if she or he is a GOOD Recruiter, would have spoken to you about. BUT First things first: You must pass your MEPS after your packet has been approved. [You will be notified if your medical waiver is not accepted]
Any specific questions I would be most happy to answer. You may PM me, if you wish. GOOD LUCK and Welcome to the Army Nurse Corps! Why doncha' check out the ANC website?