Funny, I see the coffee analogy the other way around.

I love coffee with cream and sugar (sweetener), and I love riding fixed gear; so, to me, fixed gear corresponds to coffee with cream and sugar.

I consider geared bikes and single-speed bikes, because of their lack of feedback and controlability, the black coffee, without the character and subtleties of flavor that cream and sweetener reveal in coffee.

If in the original poster's place, I would start out with a fixed gear and a front brake, and forget about the single-speed altogether.

Look at a Surly Steamroller Complete, and ask the bike shop if they'll put a bigger cog on the hub for you as part of the deal.

For gentle terrain, meaning no long, horrific hills, I consider 72 gear inches or a little lower good for someone learning about fixed gear.

Pre-assembled fixed gear bikes tend to come with a 48 tooth chainring and a 16 tooth cog, which, with 700 X 23 tires, gives 78.8 gear inches.
A seasoned rider on gentle terrain can handle 78.8 easily.
A new rider might find this a little intimidating at first.
And then again, he or she might not.

Myself, riding in hilly terrain, I went up to 82 gear inches the first month without trying, and FLEW around town.

Consider an 18 tooth cog for 70 gear inches.

This will let you cruise comfortably well above 15mph, the speed at which world class milers run the four minute mile nowadays.

I prefer a 47 tooth ring and a 17 tooth for 72.7 gear inches, but I doubt if a bike store will change both ring and cog for you, without charging you significantly more.

Also, consider putting a flat resistant tire on the back wheel, such as an Armadillo or a Gatorskin, and save yourself changing a few flats.

I've never had a front tire go flat on me, but now that I've said it, I'll probably get two in the next week.