I think 4 wraps for ds may be enough if you are going to wash everyday - I did that mainly because it was good to have routine and it made air drying them easier in the winter. How big do you think your baby will be? I had big babies so didn't do the newborn wrap thing, didn't need to but if you think he will be small then it's worth the investment.
What nappies are you buying? Probably 16 minimum for your dd and 20 for your ds but again it depends whether you are happy to wash every day. I had a nappy bin in the nursery and one in the bathroom (I just used ordinary pedal bins, plastic is better ime) so I could sluice the poo and dump straight into the bin. With bf poo I didn't sluice, but regardless I stuck them in the machine and did a cold rinse then washed them.
I have a huge bundle of nappy and wraps in size 2 to sell, they are very good nappies so not the cheapest if you are interested.