Visa. No idea, it depends upon your job. You probably will get an ARC, somebody at your job will need to sponsor you, and they'll help you set it up.

Cell phone. If you're only going to be here for 6 months then just a get a Korean SIM card (they have monthly payment plans). It might be a pain to find one for HTC though, you'll probably need a friend who speaks Korean to find you one. It would be different if you had either a Samsung, LG, or iPhone.

Bank account. Bank of America doesn't exist in Korea, so you'll probably need to pay large transfer fees to get your salary deposited there. However you can use transfer money from Bank of America to Wells Fargo and then withdraw the cash here in Korea. Honestly if you're going to be here for just 6 months then just bring cash. You can bring up to ten million won (about $10,000 USD) through customs.

CC. If you can find one that waves fees (not just international fees but also just the normal transfer fee that deposits your salary) then you're probably fine with an international card. Just be aware that smaller companies might not accept international cards, so you'll need to carry cash.

Car. Yeah you will need an international drivers license. But honestly for a 6 month stay its not worth the hassle. Korean public transportation will probably be much better than you're used too.

Social. Eating alone isn't taboo at all for foreigners. Its just that Korea has a strong group culture. If you make even the slightest effort at learning Korean then chances are very high that your coworkers will make a big effort to include you in social gatherings. You'll be fine for meetups, 33 years isn't that old ^ ^ Us expats tend to be more open-minded than average.