That is odd that your hematologist is against another pregnancy, everything I've read shows this disorder is not a factor on whether or not you should have a child. I'm not a doc so there may be things I can't take into consideration such as your previous pregnancy history. Hope you get a 2nd opinion.
My counts usually stay around 40-50 thou. During my 1st and only pregnancy they went up to 90thou and stayed there. I have an idea about most recent your pregnancy. From what I understood from my doctor is that because a fetus is something like a foreign body, an immune system may react to it affecting a platelet count possibly upping it's defense and killing off more platelets. I wonder if during your second pregnancy something went on to affect your immune system or perhaps you were eating something that thins the blood. Have you seen the list of things that ITP people are not supposed to eat/drink/medicate with? It's a mile long, maybe you were ingesting something on there and it's affect was more pronounced during pregnancy (again going back to your immune system being on red alert w/the baby on board).
Okay so I don't know if any of that was helpful but let me get back to your questions. I had my spleen removed without any real change but my count does seem to stay at the 40-50 thou range. I have gotten down to 6,000 but I got Rituxan after that and bounced back. My splenectomy was over a decade ago and at the time my doc said there was about a 50/50 chance that the spleen was the problem. I think the surgery has fallen more out of favor, but again, I'm not a doctor.
Not sure about the count threshold that could affect the baby bleeding in the brain. I was told I would have symptoms if my count got to low therefore putting the baby in danger.
Not sure about the breastfeeding either, I think new mommyhood wiped my memories of my counts while breastfeeding, great question tho!