I won't claim to know it's specific value, but I'll say this - the 912 is a NICE bike. I'm not sure a new, modern single speed for the same price would really be better.
That said, it's a moot point if you really want a single speed. You could buy the Miyata and convert it, but you may not be up for that if you are that much of a noob.
As for the hills... some here will disagree, but I don't consider that an issue. I tackle plenty of ridiculous hills around here on my single speed, and I'm nearly 40, scrawny, and I eat like **** and drink too much. If I can handle it, anyone can.
I say since you've ordered it, give the single speed a shot. If it really doesn't work for you, Fyxation makes a pretty neat kit for adding gears to a single speed. Good luck, and of course... post some pics of the bike when it's done.