Quick bike question mtn vs road bike and gear ratios

Hi all,

I am currently riding a Specialized hybrid bike. 

So it has a Mtn Bike crank ratio and big fat tires (though without the knobs you find on a trad mtn bike).

I understand that the gear ratio on a mtn bike is very different from a road bike so I am at a real disadvantage.  Also the posture on my bike makes me into a human sail.  Finally the fat tires (more surface area) can't help.

So am looking for a road bike.  Second hand for now as I am not ready to drop a grand or more on the equipment quite yet (let’s see . . . )

I see lots of road bikes (ten speeds mostly) on Craig’s list. 

First question - is a ten speed something I don't want to touch (and instead save my money for a new bike in a year)?  Bottom line - are the min and max ratios between today’s 21 speeds and yesterday 10 speeds the same?  So the difference between the 10 and 21 speeds is more variety (a wider choice) of ratios BETWEEN the common mins and maxes?  If that’s the case I can go 10 speed as I don't need the variety of choices - just more power for my crank.

My second question is, I see lots of early '90 road bikes for sale on Craig’s list.  Other than probably being heavier than today's bike, are there any real other differences?  I'm not interested in shaving seconds off my time - so the minor refinements over the last decade (assuming minor) is not that big of a deal right now. 

Thanks

-Peter