Best type of diet for an indoor 8 month old male.

I'm looking at different combinations of dry and wet. Up until yesterday he was eating 1/3 to 1/2 of a large can of wet food in the morning, the same at night with dry food throughout the day. He threw up yesterday, which made me be concerned he was overeating because my parents cats tend to overeat and he also weighs 9 pounds at 8 months old. He has also begun to shed due to him being a longhair in Florida and I feel that may have a hand in the problem as well. An associate at Petsmart suggested that I cut down on the wet food and get a better brand of indoor cat dry food that helps with hairball control. Done that so I'm wondering the best food combo. Dry during the day and wet only at night is what I'm thinking, but I don't know if his weight is healthy for his age and size and I don't want to underfeed him either. 

I wouldn't take nutrition advice from a Petsmart associate, but that's just me. Unless he has a health issue and your vet has recommended otherwise, it's actually a lot better for his long-term health to eliminate the dry food completely, and feed him only grain-free wet food if possible. If he happily eats wet food, you're doing him a huge disservice by taking it away.

There's no cut & dry answer to what a cat should weigh at what age. When you look down at him from above, you should see very slight dip inward at the waist. Looking from the side isn't too helpful because most cats have a bit of a pooch, even underweight ones.  And with a long-haired cat, you will have to smooth down the fur, or run your hands down his sides from above to feel for the waist, because all that fluff can make him look bigger than he really is.

Hairball control food doesn't stop shedding, as far as I know.  It is simply formulated to help them digest the hair that they ingest better, which I take to mean it has more oil or something of that sort in it.  But I don't think it really prevents shedding.  (if only )  For shedding, you really need brush them, especially if they are long haired cats.

And I totally agree that feeding canned would be your best option, rather than feeding only kibble.  The extra moisture in canned is so much better for them, all the way around.  Check out these articles: 

http://www.thecatsite.com/a/choosing-the-right-food-for-your-cat

http://www.thecatsite.com/a/what-makes-the-best-canned-cat-food

http://www.thecatsite.com/a/grain-free-cat-food-what-does-it-mean

Hairball control food just has more fiber in it, usually from grains. So you're literally paying to clean out the litter box more often!

Wet food helps with hairballs. When I started on a 100% wet diet hairball vomiting episodes went from a couple times a month down to a couple times a year. This was with a longhair.

Get a deshedding tool like a Furminator to keep shedding down to a minimum.

Others on the forum use egg yolk lethicin for hairballs. It breaks down the fats in the hairball so that it can pass through the body in the stool easier.