Ive always read to use OEM friction plates. I think GYTR is a good brand too. I think it is considered OEM. Correct me if I am wrong.... Also make sure to soak your new plates in oil over night before you install them.
Don't mean to chime in, but I hear HMF is highly recommended in the exhaust world. If you wanna spend some money the Pro Circuit T-4 is a great pipe. Had it on my Kawie and sounded great and added some power. About the clutch, like he said, stick with OEM and if you want a bit more performance go with a GYTR because that's still yamaha its just their race brand. EBC is good but you'll never find anything like the Yamaha kit.
HMF is nice but if you want the most power increase get a Curtis Sparks or CT Racing single exhaust. If money isn't a issue then go for a dual set up like a LTE or Barkers system. I got my Sparks full exhaust used cheaper than you could buy a new HMF system. Defiantly go with a full system and not a wimpy slip on. You will also need to upgrade your intake and carb jets when you upgrade your exhaust. Pro Designs make a great affordable intake for the rappy.
My bad you have a 350 and not a 660. Barkers doesn't make a dual setup for your bike. DMC does tho. Its called the Alien. But you wont see a huge increase in power like us 660 and 700 owners. My buddy has a HMF full system on his 350 is sounds really good. Since power increase isnt gong to be a big option on the 350 I would just hunt around for a good price on a used one.