I have to say that I have never known a cat in a a caring household to starve - they are not backward in letting you know their needs - the only time i have found it necessary to regulate food is when a cat is still eating for Britain but is getting less exercise.
I'm not familiar with the tins more the pouches. My mum feeds her cat the Felix tins and its one tin a day in three servings as her cat is a bit of a glutton. Just have a look at the content at the back of the tins. If he's a big cat already, is this big cat/fat cat or big cat/muscle cat? If the former you may want to consider the food he's eating as these tend to be higher in fat (slightly) but if he's active it should balance out.
It depends on the food and the amount of biscuits you give. If you imagine biscuits are just the wet food buy dry, so lots of that will probably compensate for small amounts of dry food.You will see how much to feed a cat by weight (usually) on the back of the bags.Careful with fat/oil contents with some foods. Too much will produce a more rotund cat (like mine ). You just need to balance it out.What are you feeding him?