all this is really good advice, especially the doc approval stuff...
if you think that you might enjoy riding for more than commute, try an used hybrid and look for rack braze ons on frame and fork, then you could go on holiday by bike too...
wanna keep it simple try finding an old freewheel hub for the rear and make a single speed, i ride a mile to and 1.5 from work on my home built hybrid fixie, and have gone just under 20 for fun (still working out kinks of bike and technique)

at any rate imo fit, comfort and fun are the most important things to riding. make sure whatever bike you find it fits you properly, and no you don't have to go to a bike shop for this, try your friends, library or bookstore and look for books on bike racing, touring and training, somewhere inside will be any number of different formulas on how to measure yourself and fit a bike (don't be intimidated, people still can go to a tailor to be measured for clothing and get a better fit than off the rack clothing and its the same with a bike), the frame's dimensions should be discussed around these measurements. if the bike's fit is off you won't be comfortable and thusly not confident and less likely to ride...

and i think that we will all agree that is not fun

good luck