Hills, Hills, Hills

-- I am not sure what type of bike to get?
This is always a tough question, and the reason I have both a road bike and a mountain bike. What kind of off-road trails might you be riding? Do you think you will need a front suspension fork for the trails? From your description, a cyclo-cross bike might be the best choice for you.

-- Can I retrofit a rear rack on any bike?
Yes, more or less. Lightweight racks clamp to the seat post, while more heavy duty racks bolt to some bike frames.

-- Even assuming road bikes are quite better at climbing hills, would a more expensive mountain bike be better than a lesser valued road bike (since used mountain bikes tend to lose alot more value than the road)?
It depends on if you really need a "true" mountain bike with a suspension fork. The bobbing action and weight of a suspension fork is a detriment on hills, but some forks are equipped with a lockout feature. A light weight mountain bike with a lockout fork and slick tires can perform quite well on the road.

-- Are disc brakes worth it, or just a gimmick, because when I was young I was more reckless, but honestly I feel trepidation thinking about riding down all these steep and vast hills in my area? When I was young I over-estimated drivers, now that I drive myself, I know that drivers do not expect to see bikers.
Disc brakes on mountain bikes are great for wet or muddy conditions, but many still use rim brakes for their simplicity and lighter weight. Rim brakes rule the road.

-- Is using a bikepedia.com a good measuring tool of a how good a given bike is, by trying to found how much it sold for when new? Ex. A bike that sold for $800 new in 2006 should be better than one that sold for $500 around the same period.
I like using bikepedia for comparing different bike models.

I went to two local bike stores, rode a couple of bikes and asked a fair amount of questions. The salesmen at both stores both said that mountain bikes tend to be better for climbing hills, they tend to have more gears in general and more lower gears than road bikes. One salesman also had me to check out some hybrid bikes, but I did not like them too much compared to mountain bikes. That same salesman said that for hills you want a sprocket with small gears in the front and a back sprocket with lots of teeth.

At the second store there was a small hill in the parking lot I used to test hill climbing and changing gears on hills. I tried a 21" Trek 4300 disc($529) with a lockout fork and it seemed to change gears more smoothly than the Trek 4500($619) with some kind of Tektro V-brakes. I figured before that if I used price alone to compare it would mean a better ride, especially considering that this test scenario was using V-brakes which meant even more money to go to a higher end gear shifter. The shift lever seemed fancier on the 4500, but it would not shift smoothly most the time and I almost busted my nut on the little hill when it miss shifted.

@Scotty_Dog: Cyclocrosses are considerably more money. At the Trek/Specialized shop I asked about them and the cheapest they had was $960 and the salesman said they involve more precise engineering and cost more. He also said that they are not as good for climbing and tend to have less gears, especially lower ones compared to mountain bikes. I kind of regret not asking to try that Cyclocross anyway provided it was close to my size. There are some used in my area listed on Craigslist for $1100 and $800!

I am leaning against Craigslist as time passes, people there are often mutants, they leave little info especially on frame size, model year, if they take pics at all they do not host them elsewhere in high resolution, they sell the item and don't delist, often they ask too much $, etc. To give some small examples: I found a Gary Fisher Piranha listed for $350(new retails at $800 or more) but the guy sold it and didn't delist. I found a Trek 1500 road bike listed for $250(Bikepedia has them in the 1,000-1,100 range) an unbelievable deal by Craigslist bike standards that I regret not pouncing on provided it was my size. But I emailed that guy April 9th and he said it was sold, but he still has that ad up, even though I told him how delist it. I am gonna give Craigslist or Ebay local two more weeks tops, then I will just buy new 'cause I do not want to miss the good weather without a bike.

This has me leaning toward a hardtail mountain bike with a lockout front fork.
I am thinking of maybe ordering from bikesdirect(free shipping) a:
Motobecane Fantom Trail Mountain Bike $595.95
It has excellent components for the price that I would not be able to afford otherwise. The only thing is I cannot test ride. But generally the guys at the stores never had me look at anything below 19" frame.

A lot of your experience with Craigslist is probably local to you. Here in Virginia, I just bought a Bridgestone MB2 for $60 and have it pretty much serviceable for another $150 or so.

Then two weeks ago, I picked up a pair of Trek 4300 bikes for $100 each, virtually unused from a husband/wife that just never got around to using them. The mold line was still intact on the tires.

It can be hit and miss, but I've had pretty good luck so far with Craigslist, and definitely like my bikes.

I still have not decided or can't. I found [ame=[MEDIA=youtube]81LgeJMy3Hw[/MEDIA]]this Youtube video[/ame]:

That guy started off with a Diamondback Insight 1(Performance Hybrid) from D1ck's. Then he tried a Local Bike Shop and got a Specialized Crosstrail Hybrid, but it did not feel good in the dirt, he returned that. The he went for a Fuji Nevada Mountain Bike with lockout fork, but it still moved about a 1/4 inch losing momentum and he did not like the upright position either. It was good offroad but he never really liked it on the road. Finally he got a 2009 Motobecane Fantom Cross with carbon fork for $799 at Sportymamabikes(ebay store).

He seems to fit my criteria almost, except for the hills. His idea of buying and trying bikes is the best, but very expensive since he had to pay a restocking fee. I definitely cannot afford to try several and pay the 10%.

This has me strongly considering Cyclocross like Scotty_Dog recommended, I should have rode one at a local bike store, but I told my price range first and the salesmen dismissed other types of bike that are pricer like Cyclo and I did not push the issue. Next time I need to avoid discussing price range till I can try one.

Questions:
1) What posture is more bio-mechanically efficient for uphill, the more horizontal posture of a racing bike or the more upright posture of a mountain?
2) Some have advised me that a mountain bike is easier for hills because it has more gears and specifically more lower gears, but others have said this is actually a hindrance because most the enormous gear range is useless for climbing hills on road. So what is it exactly?