I would say it all comes down to how much power he wants and how far he wants to push to the edge. If he is wanting to go supercharger, the Roush blower is a great blower and you do have the option of keeping the factory warranty as long as it is installed by an authorized Roush dealer, which in Columbus is either us or Krieger iirc. Roush charges a $300 fee to retain the warranty and it is handled by Roush from there on out. You do have to run their tune to keep the warranty.
There is usually plenty of power left on the table with the Roush tune. For example, a Stage 3 (which they rate at 575hp) will usually make 490-510 rwhp. With a cai upgrade and tune, we typically see about 80-90 hp gains which is plenty for the stock bottom end in my opinion. Aside from that, a clutch upgrade will probably be needed if he plans to run it very hard and depending on how far he would want to push it, billet oil pump gears also become a good idea.
If he is wanting to stay naturally aspirated, a tune and maybe gears (depending on what is in it currently) is about all I would do. The stock airbox flows really well, so there is minimal gain with a cai. There is a tad with an offroad x or h but again, not enough to justify cost in my opinion.
Everyone likes to bring up the trans. There certainly has been some issues but no where near as many as everyone would have you believe. I wouldnt worry about it too much. We do a ton of these cars and havent had any trans issues other than some stock clutch failures. Ive also beat the living daylights out of our test car. I broke the driveshaft, the limited slip, and seperated the stock clutch from the pressure plate. The trans still works perfectly fine. The biggest issue really is the clutch not disengaging at high rpm. As power comes in harder, the issue becomes more pronounced. Upgrade the clutch and that becomes a non issue.