I want to say that I am no expert, so please just take my advice lightly.
1. If I want to get pregnant I need to stop nursing my 7month old in order to bring back ovulation?
You can get pregnant while breastfeeding, it's just a lot harder if you don't have a period. What he says about not ovulating while nursing is usually true. There are some cases though, where women do get pregnant without the return of their period. I would guess (only my own guess) that they caught the egg at the beginning of what would have been their first PP period. Some women also get their period while breastfeeding (myself included, 2 months pp both babies and I did/do breastfeed). If you don't mind waiting it out though, it is possible to get pregnant breastfeeding.
2. Once I get pregnant, they would ask me to stop nursing because breastfeeding while pregnant can cause miscarriage??
As far as I know it can, but very unlikely if you normally have a healthy pregnancy. I am no medical professional though. An example, since I am high risk because I give birth to premature babies, I would not breastfeed while pregnant even if I wasn't advised not to. Breastfeeding does cause minor contractions.
3. He said to just wait for a few months and see if it comes back and then go from there. He said taking OPKs won't do anything because I'm not getting a period/not ovulating.
It is true, you do need to have a menstrual cycle to ovulate. However, your cycle can return at any time while breastfeeding. It just takes awhile for it to return for most women. Also remember my answer from the previous questions in reference to this one.