This varies - in my case it took about 4-6 weeks for my blood pressure to return to normal. Everything else (e.g. liver enzymes, protein etc) normalised in a couple of weeks. Some women find it takes longer for their blood pressure to go down again after very severe pre-eclampsia.
You should probably ask your docs re: ttc but I tried again as soon as periods returned (about 10 weeks). I was 38 by then so hanging around waiting was not the best idea. Many women try again quite quickly, especially as (like me) I don't think you had a surgical delivery. You might need iron supplements - I look pregaday (iron and folic acid) all the time I was ttc.
Hope this helps a little