Buzzard is probably right, the problem with small stones is that there are so many of them and they, being small are more difficult to look at individually and from rough they are difficult to polish to the same kind of standards as larger stones. The three things that you would look for in a diamond; cut, colour and clarity are, as others have said, the key. What is difficult to establish with so many stones in a single ring is the clarity or indeed the colour of each stone because each one is so closely linked in the setting to a whole bunch of other stones.
I think that you would get better value from an independent jeweller or antiquarian specialist who is not relying in buying high volumes to reduce prices- go for something unique- as this is a really special ring it does not have to be more expensive but it will be more unusual. Take some time to find what you want within your budget. You could have fun finding the biggest, nicest eternity, solitaire or cluster you can afford.
Some people don't like the idea of antique jewellery, personally I would like it more knowing that it had some kind of provenance or history. I have a ring with 18 smallish (1.6ct) diamonds in the shape of 3 daisies , it was my grannie's, given to her by my grandfather whose mother had given it to him. When I got it I really did not understand what was special about it, or appreciate it but as the years have gone by I have grown to know every stone in the ring. I know where all the inclusions are, all the cracks and imperfections, I can see them with the naked eye because I know them so well- I can see that one is greyish, another blue, a third has a yellow look etc. This might all leave you cold, but you wanted to know about diamonds... you develop relationships with them. They burn like fire sometimes, you can see the whole room reflected in a single facet if you look carefully, yet the facet is only millimeters in diameter.
I hope us lot have not put you off, but instead have spurred you on to enjoy the process of finding the right ring.