"Fit" is another matter, and it implies "for a purpose" or toward some goal.
I'd start with a mix of body composition (your body fat percentage, nut just scale weight, and certainly not some crap bogus metric like BMI). You can come up with a pretty good estimate just by eyeballing, or you can take tape or caliper measures and run them through a model. A good online site for same: http://www.linear-software.com/online.html
If you want some fitness basics a good start is here: http://liamrosen.com/fitness.html
For books, "The New Rules of Lifting" is decent. You can do the workouts at home, though a gym helps: http://www.amazon.com/New-Rules-Lifting-Maximum-Muscle/dp/15...
I actually prefer a good 5x5 program for beginners (simpler, brutally effective). Check out http://stronglifts.com or look up Mark Rippetoe's Starting Strength .
Fitness metrics: body fat, strength, speed, flexibility, endurance, heart rate, lipids, etc.
I've worked in tech for 20 years. I've contributed to some major open source projects and worked at some significant organizations. I've also taken fitness pretty seriously after letting it slide. I do lift weights, hike, bike, swim and row. What you do with it is up to you, but I've found that the investment pays off very high dividends.
I've eaten at a McDonalds once in the last 20 years. That's not food. Neither is Coke refreshment.
If you want to understand what's what in fat loss, Alwyn Cosgrove's "Hierarchy of Fat Loss": http://alwyncosgrove.com/2010/01/hierarchy-of-fat-loss/
TL;DR: fat loss is about diet. Yes, diet. Strength training builds/retains muscle, so do it. HIIT cardio helps some, steady state cardio a bit as well. But really, it's mostly diet.
If you want to understand more about this, you could look into starvation literature. On a reduced-calorie-only approach, about 25% of your weight loss comes not from fat but muscle. Which is among the key reasons diet-only approaches fail. Among exercises, it's strength training which builds muscle, not cardio, which is why a running-only exercise approach won't get you ripped either.
This is also a major reason why I find the emphasis on "weight" loss in both mainstream and medical literature immensely frustrating. What really matters is the relationship between two tissue types, subcutaneous fat and skeletal muscle. They're gained and lost through very different mechanisms, and play very different roles in body function. Confounding both as "weight" is an immense disservice.
For a plan putting this together, there's The New Rules of Lifting, or for the gals, The New Rules of Lifting for Women. Exercise plan, diet, lifting, cardio, a ton of info on what goes into fitness. http://www.amazon.com/New-Rules-Lifting-Maximum-Muscle/dp/15... and http://www.amazon.com/New-Rules-Lifting-Women-Goddess/dp/158...
If you want a simpler, and IMO more effective beginner's program, Mark Rippetoe's Starting Strength: http://www.amazon.com/Starting-Strength-2nd-Mark-Rippetoe/dp...
That's based on a classic 5x5 lifting program. It's simple. It's effective. After the first few weeks, it's pretty brutal. But for a novice trainee there's hardly anything more effective.