Okay, got it. Well, what i would do, i see what clientele i sell to more and focus on that group. So if online is your thing, i would indeed splurge on a negative specific scanner, given that flatbeds don't have the greatest reputation for scanning negatives (although some would disagree). The reason i say this is because bay photos metal prints are awesome, and look better the larger they are.
Now, I'm not a business person, but the metal prints aren't cheap, and unless your selling several a month, i think you would offer the customer more bang for their buck by making fiber prints (at least from a collectors standpoint). this would also put more change in your pocket. Now, some don't enjoy the darkroom as much as others and if you don't, i wouldn't bother investing heavily in darkroom equipment. If your doing good selling digital color prints, and you'd like to add your b/w work (coming from negatives), i would stick with scanning.
to answer the second question, you could potentially get more information from scanning enlargements, but what you want to get is grain detail when you scan b/w, which is what makes b/w so great, so your best bet, is to scan negatives, not prints.
Now if you want to wet your feet with b/w darkroom printing, i say go for it and i definitely don't discourage it, but only you know what is financially sound for you to do at the moment. One thing you can do is get a cheaper enlarge or look on craigslist. which is where they are sometimes (more often now than before) being given away for FREE. The enlarger itself, might ease things, but what you really want is a good enlarging lens. 90mm or 105mm enlarging lens is what you need for 6x7. i personally use a 23c that got for 100 bucks, and it came with everything else needed in the darkroom.
how large do you plan on printing in the darkroom?