Own root (mostly; you can find a few grafted).
Depends on the variety. Some are small, some get to be floribunda sized.
Bloom: depends on the variety. Some are the same size as miniatures, some are like smaller hybrid teas.
Disease: all need to be treated for blackspot here.

I just saw Richard Anthony (For Love of Roses) last weekend, and I have a friend who is working with him. He is striving to keep many minis and minifloras in commerce, and you can't go wrong with any of the minifloras on his list (Nancy Jean and Leading Lady are borderline tender, and also have huge blooms). There other vendors are Burlington Roses, Heirloom Roses, and Roses Unlimited.

I have grown Olympic Gold for many years, and I love Conundrum. Whirlaway is stunning.

I grow about 20 miniflora's. Like Diane says, bush and bloom size depends on the variety. It usually takes a good 2 to 3 yrs for the rose to get established and really show it's merit. I've also grown Olympic gold for many (early 1990's) years. Conundrum and Whirlaway are great roses. Low and Behold is a beautiful yellow. I've had Tiffany Lynn for over 20 yrs. It's a beautiful pink blend. Cooper is a beautiful deep red. Dr John Dickman is a good lavender/purple. Sweet Arlene is a really nice soft lavender. I really like Regina Lee. A beautiful white with red on the petal edges (like a small Double Delight). All of the venders Diane listed are good. For Love of Roses sends large plants. Think Palatine compared to Pickering. Before buying, check each rose for winter hardiness. Some are very tender. Do a little homework before buying and you'll be happy with the roses you choose.

I have 15 minifloras now. I like them because the plants don't get as tall or big as the HTs do but for the most part they have that bloom form. They work very well in my patio pot garden. All of mine are own root and I've gotten them from many different sources but Burlington and John's Miniature's (now through Heirloom) are the two where I got the most I think. Since I've been maxed out on room of late I haven't gotten anything from For Love of Roses yet but I peruse their web site often and I'm sure an order is soon in my future, lol!

The class was started mainly for exhibition purposes I believe. Hence the nearly always exhibition form. There were some newer minis coming out that were just too big to be shown as minis and/or would simply out shine the minis because they were bigger. So they started to call them minifloras, somewhere between a mini and a florabunda. The ARS didn't immediately recognize it as a class and the term "miniflora", all one word, wasn't sanctioned until a couple of years ago. Before then there were several different spellings.

As for sizes you have to remember that the classification of a rose is soley up to the breeder. So if the breeder says it's a miniflora, it's a miniflora. Whether the bloom is 1, 2 or 3 inches in size. It doesn't matter. So there is a range of sizes for plant, leaf and bloom. As a general rule of thumb minis are usually around 1 to 1 1/2 inches in size up to 2 at the most. There are a few bigger ones because they were classed before minifloras came into existence. Minifloras generally range around 2 inches but can go to 3. Florabundas are between 3 and 4 inches and HTs can go from 4 to 6 inches in size. But there are exceptions to all of that. For the most part breeders are careful to place things in the right classes but sometimes there are reasons for putting it in a different class. It happens.

As for what I like best of mine, probably First and Foremost as a garden plant. It blooms almost non-stop for me and i love the bright cherry red color. As a show rose I'd have to go with Snow Ruby because I've won Queen of Minis twice with it!

Thank you so much everyone, there is some really good and detailed information here and I do appreciate it. I have been impressed with the looks of minifloras and would really like to try them. The smaller size plant appeals to me also.