RW,

First question is hard to answer. Small jars are usually ready to apply. Larger quantities are usually thicker. For brushing, 50-50 is usually good. For spraying, you need more thinner. How much depends on your equipment. I prefer brushing for a "decent" finish. Spraying is a lot faster though.

First you must sand the plane VERY well. Put on three coats, sanding between coats. You will get raised grain so you must sand well. Assuming all is well (smooth and level) apply one more coat without sanding.

Now you apply silkspan. I apply mine wet. Make sure you run the grain spanwise on the wings. Many people apply silkspan over all balsa surfaces. This gives a smoother finish with less effort.

I use thinner to apply the silkspan so it will adhere from the bottom by softening the last coat of dope you applied. When it is dry you can apply enough coats of dope to seal the silkspan. Sand between coats after the second coat. Be sure to sand only to the silkspan, don't sand through it, especially at wing ribs. If you do sand through, a thin coat of Brodak Rejuvenator can sometimes rescue the rip.

Next apply several coats of sanding sealer to fill the silkspan, sanding well between coats. Apply one more coat of clear, then a blocking coat of gray. The blocking coat prevents your seeing brush marks through the wing panels when the sun shines through it. It also allows you to use fewer coats of color.
When you apply color, start with the lightest colors, then do darker ones. Some people apply the lighter color over the entire plane, then apply the next color, etc. A lighter way is to mask off all that is not going to have the lighter color, then mask for the next color, etc. (Mask whatever you're not painting).

Make sure the dope is thoroughly dry before applying the next coat. This is especially important when applying color.

When brushing, make sure the brush stays "wet" otherwise the dope drags off the brush into the dope. Keep the brush moving fast and don't brush over the same area too long, otherwise ... hairs.

Of course this is only one way of doing it, there are infinite other ways.

I'm sure others will supply alternatives that work for them. Choose whatever fits your needs.

Good luck,
George