I read the other day that eating peaches, apricots, plums or nectarines could reduce insulin resistance. Any advice about how many per day?  

Variety, not number. The fruits you mentioned have a relatively low glycemic index, i.e. They won't cause the high sugar spikes you can see with other fruits. Common questions people have: will eating those fruits prevent diabetes? Will eating lots of them treat diabetes? No and no. Rather, they are good alternatives to more sugary fruits. You still need a good variety of beans/legumes, healthy meats and veggies.