I am very interested in the answers to your question as I am going to try budding soon.

It's a somewhat complicated process with TONS of info about it online. But here is a great source of info on the process. http://scvrs.homestead.com/BuddingUltimate.html

I will tell you however that you'll need both the bud sticks and the graft cutting to be at least as thick as a pencil or it simply won't work. The second best advice I can give (and this is what made all difference between failure and success) is that when you cut off the bud, all the tissue must be green. No white or very little white. When you make the wound, it too must be very thin. The most important thing (next to it being as steril as possible) is to be sure that the contact is green on green. 90% of failure is because people cut it too thick into the white tissue. It takes practice to cut it very thin.

Oh, and to answer your questions:

How many scions do I cut per rootstock? I'd say 4-5. You want to heighten your chances of one sticking without mutilating your root stock so bad that it can cause it to die back (at least 1/2 inch between buds)

-How large does a rootstock need to be before budding it? At least a pencil in diameter and usually more than 4" tall

-Does it matter how old the rootstock is? for instance is it too old if it has flowered? No. One that has flowered is ideal but as long as it's healthy it really doesn't matter the age the diameter is more important (from pencil to crayon in thickness). Also your root stock must be well rooted otherwise it's unlikely to stick. Unless you're an expert, understock must be well rooted first.

If it helps, traditionally, the stocks are struck in the field in summer to fall of one year, then budded the following summer. I have rooted stocks over winter and budded them a few months after they have been potted and show vigorous growth. I have also budded scions to stocks which were several years old and previously unused. I have also budded scions to seedlings, both those raised the year they were budded as well as many which were several years old. The only real "requirements" are the stock must be at least as thick as the wood from which the scion is removed, or thicker; and the stock must be in vigorous growth, showing a lot of new growth being pushed. That alerts you that there is good sap flow, permitting the bark to lift more easily and to maintain the scion with sufficient sap flow until the two pieces knit together when the stock will support it as it does any of its own growth.

If your goal is to produce a "commercial" budded plant, you probably only want one or two scions per stock, budded on opposite sides from the other. If you're practicing budding and as long as the scions take, the number of scions inserted in the stock is only limited by how much room you need to bud them to the stock. I've successfully inserted a dozen scions in a long whip with them all taking. The advice above is also good. You don't want to destroy the stock and doom any potentially successful scions above the mangled section.

If your goal is to establish a rose in your collection, keeping several long, rooted whips around, ready for budding, can help. I had budded Souv. de Therese Levet to a seedling, then accidentally ripped the more vigorous growth from the stock. The remaining growth and seedling died, but I was able to insert seven buds from that separated growth into a long whip of a seedling, with all seven succeeding.

If you're going to the Heirloom Expo, Jeri has an own root, virus indexed IXL and a virus indexed De la Grifferaie she picked up from me yesterday on her way up. Both root easily and have been treated and tested by UC Davis to insure they aren't infected with RMV. Both would make excellent stock mother plants to root succeeding generations of stocks from, and both root fairly easily. Both, like Pink Clouds, can either be "T" or chip budded. Chip budding is the easiest and fastest method for home use. As long as the scion material is in good shape, I average nearly 100% take with chip budding. Good luck!

p.s. what is a rose"whip"??? Lux.

A very long root stock. I often root one, two up to four foot long sections of de eyed canes which I will either use to produce a standard or to bud multiple buds of the same rose on to get it established. Once there are a few takes, it's simpler to reproduce it on the size desired.