IMO the biggest weak link is the soil many of us use. It is usually the catalyst for introducing bugs. But we can’t really control that as it’s trial and error and issues can pop up at anytime. Even if it’s kept in ideal situations.
The biggest source of a bug infestation, at least in the Pa/Ohio/WVa area, is bringing the bugs in when transferring from outside to inside. There aren't too many critters in this area that cause problems other than white flies and sow/potato bugs. The white flies (I don't know their proper name) live on the underside of the plant's leaves and are surprisingly good at staying hidden, coming out when the lights switch on/off and if you shake the plants. They are small and hard to get rid of. When allowed to continue, they cause small weeping areas on the buds, which leak sugar-ish water that carbonized when burned. The result is a sub par appearance and taste with a lot of black ash and lousy burning. I burn PIC mosquito coils to eliminate them after turning off the fans for an hour or two. The sow/potato bugs look like a small gray armadillo type of bug, that curls up into a small round pellet when disturbed. They eat the roots off of plants and live in the soil. I have used a couple of drops of Malathion mixed with a gallon of water and watering the plants with it. It stinks but is pretty safe and breaks down quickly.
There are a lot of different pests found in different regions. I am fortunate that we don't have much in the way of mold/mildew problems or some of the critters I hear of out west. Winter kills off a lot of the problems and I have "baked" soil in the oven to make sure everything is gone that needs to be gone. Keep this thread going and hopefully we can get a list of bugs/critters, where they are, and how they are dealt with.