Re: getting early advice
It's very likely that your supply was low as a result of the other problems. If your son did not have a good latch and remove milk efficiently in the early weeks, you probably didn't establish a strong supply.
Tongue-tie can be genetic, so I'd suggest having someone check your next baby's frenulum right away in case it needs to be snipped.
The best cure for a low supply is just nursing nursing nursing! Some people also swear by fenugreek or other herbal remedies.
I think you're smart to line up some good support now. Maybe start attending LLL meetings (pregnant moms are welcome, and you can bring your older child). Find the name and number of a good LC who can help if you have latch problems.
One other idea is to make sure you have plenty of help with the housework and your older child after the baby comes so that you can concentrate on just feeding the baby.
mama to Isaac (4/04) and Flynn (10/06)