I'm so glad your little boy is here and doing well! The NICU alarms do take a while to get used to, but you will.
My BP remained very high for a while after delivery. You are so lucky the mag didn't bother you much! I was on the mag for three days before delivery and a few days after. It made me really sick. Also, after delivery they wanted me to remain lying down for a few days while they tried to get my BP to come down. I was still on the mag so my vision was blurry and I was miserably hot. I didn't even get to see my baby for the first time until a day and a half after delivery, when they finally decided I was stable enough to wheel my whole hospital bed down to the NICU. I was released five days after delivery, and although my BP was lower it was still pretty high for several weeks. By about 2 months it was under control with meds. My kidney function and protein levels returned to normal quicker than my BP, maybe within a month (I can't really remember exactly).
In my case my BP didn't really become "normal" until I was taken off the breastfeeding-safe meds (labatalol and some calcium channel blocker I can't remember) and put on regular BP meds (hydrochlorothyazide and lisinopril). I tried pumping for seven weeks while my baby was in the NICU, but I never produced more than 15ml at one session, double pumping. I think a combination of factors from my illness affected my milk production (the early delivery, the c-section, the high BP, the lack of physical contact with my baby for weeks, the stress of having a sick baby in the NICU, etc.). When my daughter was finally released I decided to give up pumping (at that point she was mostly on formula anyway) and my nephrologist switched me to the other meds, which worked much better for me. I only have one kidney so I see a nephrologist annually anyway, but they also treat chronic hypertension. He told me that he has seen a wide range of recovery times from preeclampsia, including patients who require treatment with medication for the rest of their lives. One of his other patients just got off medication one year after her delivery.
My nephrologist was happy enough with my stability on the BP meds that he said I wouldn't need to come back for a year, unless my home BP monitoring showed changes, and then he would adjust my medication. Then I ended up getting pregnant again, so that plan changed. He took me off the meds I was on (not pregnancy safe), and my BP remained low enough to remain off them for now (about 19 weeks off, and BP still stable). He said that is probably because blood pressure drops naturally during the first half of pregnancy. Currently my OB is managing all my care, and she will put me back on pregnancy safe meds if I need them again.
Postpartum OB care usually lasts about 6 weeks, so if your BP remains elevated longer than that you will need to find another doctor to treat it. If that happens, I highly recommend finding an expert in hypertension, such as a nephrologist. Even though I wasn't seeing him for hypertension previously, my nephrologist was much more knowledgeable about my condition than my family practice doctor.
Take care of yourself and try not to worry too much. It is hard leaving your baby in the NICU, but he will be home sooner than you think. For me the tough part was bringing her home. I was so used to all the monitoring equipment telling me how she was doing that it was scary at first to have her home and not have a monitor to tell me if she was doing OK
1st - miscarried at 11 weeks in Dec. 2009
2nd - baby girl born Mar. 2011 at 29 weeks 6 days due to severe PE
3rd - baby boy due June 19th, 2012