Chanz, PCOS and diabetes can both result in problems with breastfeeding, but this is by no means always true. If you concieved with no medical support it may not be a problem at all, and even if you did need medical intervention to fall pregnant, there are many women (like 1st timer) who manage to breastfeed without a problem. The problem with PCOS is that women with the condition can also have insufficient glandular tissue in their breast which means they "dont have enough milk". Even if this is the case their is no reason why you cant combine feed (breastfeeding doesnt have to be all or nothing).
If your sugar levels are under control with the insulin, then that shouldnt be too much of a problem, but I would just take extra care to eat healthy, low GI foods to keep your sugar levels stable. I would also recommend finding a leleche leader in your area and going to a few meeting before the baby is born - just to learn as much as you can to avoid common "booby traps and misconceptions"
Online there are leleche forums where there will be other moms who have faced the same difficulties who can maybe give you some support, otherwise
www.kellymom.com is a great resource and on facebook there are a number of breastfeeding groups who all chat.
You can also go see a lactation consultant - but make sure she jas the credentials IBCLC behind her name as this makes her internationally certified, a Lactation consultant without those letters may be very good, but could also have only gone on a 2hour course run by a formula company:)
Good luck and congrats on the pregnancy!