iPhone questions (again)

[lioritgioret]

In the wake of the stormy hysteria it has become apparent that at the very least I need a phone that does text messaging more handily than the current LG, a phone so plain and old-fashioned that even the workmates who barely notice me are aware that I have an hilarious antique phone.
I asked these questions last year, but I still haven't gotten around to getting the phone, so I'm mainly checking to see if things have changed.

I want an iPhone, for a variety of reasons, some of them irrational Apple fandom. Has this become any more stupid than it was last year?

I want one that can access the Internet on its own, i.e., 3G or 4G, so I can do credit card transactions at events that don't have WiFi. I might also want to be able to use it to provide internet to another device occasionally.

I might like to watch an hour or so of TV on it a day. This seems to be the most expensive thing, running 6 to 8 GB per month on the data plan. Is this nuts?

I want to be able to send emails and texts and run a couple of apps, like one that helps me track calories and exercise.

Is there any compelling reason to get the iPhone 5 instead of a 4?
Is a 16 GB phone enough or am I going to want 32 or 64?

Thanks!