Not a problem. I think the sizes of the drums will do you well for a wide variety of music. The smaller the drum you get the less bottom end you will have. You can always tune up a 16" floor tom but try tuning a 14" to have the depth of a 16"... no really go ahead and try.
If I had anything to stress about all of this it would be learn how to tune the drums. Read up
on it... or at lease visit the Evans homepage.... check out the videos. There are some excellent videos on tuning drums at that site.
Another thing to consider is that you do not have to set the drum kit up like they have it in the picture. Experiment. Swap one of the floor toms to the left side of the kit and you open up some new opportunities for interesting sounds/combinations.
I have a total of four toms... three rack and one floor.
The floor tom is to my left and the 13" rack tom is now my right side lowest tom.
I have taken my smallest drum the 8" and cranked up the tuning so that it is a little
bit higher in pitch than the snare drum (with the snares off). This was all done to increase
my range with my current rock/metal band.
Just remember... experiment.. do your own thing...