Can't help you with #2.
As for #1, I can repost the advice I disbursed on RealmsOfEvil recently:
Here's my general advice:
1) If you have not read Monte's articles on prestige classes, read them:
http://www.montecook.com/arch_dmonly9.html
http://www.montecook.com/arch_dmonly10.html
2) Before you even begin, consider whether you really need to design a prestige class. Some concepts can be acheived by class combinations, though if the class combination is rather weak, you might use a PrC to spruce it up. A general rule of thumb for me is "don't make a prestige class unless you need to."
3) If you need one, can you get it by tweaking an existing prestige class? There are a load of prestige classes out there. If one is already close to your concept, you might be able to get what you are looking for by swapping out an ability or two.
Okay, you have gotten this far and still want to make a prestige class? Hmmm, I am running short on advice now, but the next most crucial thing you can do is HAVE AN OPEN MIND. Once you start making a prestige class, it gets easy to get attached to a concept and overdoing it, and then have a hard time accepting that the class is too powerful.
Panning out abilities:
What I generally do is find the class that it is most like and use that as a pattern for BAB, saves, and HD type. For example, a monk based prestige class might have moderate bab, d8 HD, and all good saves. As monte says, if your requirements are stringent, you can afford to be generous. When assigning good saves, I would generally avoid increasing good saves unless you plan to impugn the bab or you feel your requirements have been stringent.
Class abilities: don't make any prestige class clearly better than any similar base class. That is the most basic guideline for ability selection. A fighting class with two good saves, feats every other level, and class abilities on the alternate level sound much much better than a fighter unless those feat selections are very specialized. But one with a feat every third level, a minor class ability on the remaining level and two good saves might be okay.
Spellcasting: This is the easiest part to screw up. Generally speaking, allowing full advancement only if the class abilities are somewhat tepid and/or the entry requirements are very strict. Otherwise, consider dropping a level or more out of the advancement. (Like planeshifter or some of the classes in tome & blood)
The weakest form of spellcasting advancement is to start fresh from 0 level, using a custom spell list, but with this type of list you are usually safe giving the class a few strong abilities. The sacred fist and the templar is a good example of this sort of class. Custom spellcasting lists are a good way to add a unique flavor to an existing class.
Hope that helps.
Same one as XCorvis put up.
