so long as your sides are thick enough to be cut that short and look good, and your temples havent receeded much you'll be okay.. although with a topper if your temples have receeded, you can get temple flaps (which is from what I've read) recommended if you do have temple recession.

Are the styles possible? Yep. Just look at the model at the top of the page (I forget his name)

As for hair color, if your hair color is dark then it is much easier to color match then a blonde / light brown, so I wouldn't worry about it (assuming you have dark hair). Otherwise normally the color match is very close if not spot on from a hair sample.. and yes, hair peices can be dyed to match although I haven't done so myself. On my first order John offered me a stock which was a dull blonde that I could dye to match my specific hair color. I didn't feel comfortable dyeing it so I just sent in a sample.