Colour with B&W enlarger: yes - you can use colour printing filters in the enlarger's filter drawer (if it has one).
B&W with colour enlarger: yes - you can use the colour head's filtration to select the required contrast grade using variable contrast papers.
Mirrors: depends how much white light your enlarger or door etc leaks and where it gets bounced to, but probably easiest to put a dark cloth over it to be safe.
A bit of advice. If you are looking to purchase an enlarger, go with a dichroic color enlarger. A used one is brutally cheap (particularly if you are looking at 6x7 or smaller) and as noted above, convenient for both color and b&w.
My friend is trying to figure out how to enlarge a 8x10 negative onto an 11x14 paper w/o making the print look blurred! Any suggestions? Thanks!:rolleyes: :confused:
Your friend needs an 8x10 enlarger (scarce and expensive), or an 8x10 scanner (less scarce and expensive), or a scanning service. You might be able to stitch together multiple scans from a flatbed scanner that can go up to 4x5".