An 07 as a first car, that's cool. My first car was a 79 Caprice Impala, (older then me by 5 years) and in no way economic at about 20 miles to the gallon it cost me 7 dollars a day to get to and from work. When I got my 06 TC did I get rid of the beast, no. In my opinion I don't think that you should ever get rid of your first car (if possible).
In theory you don't need a tachometer, because traditionally they were just used to gauge the safe areas of engine operation and to know when to shift gear accordingly, rev-limiters made them slightly less useful and you can tell you need to shift by sound alone.
ANYWAYs the Yaris probably has a rev-limiter to prevent any engine racing, however common sense is always best applied topically.