Alright, this is pretty long because I wanted to see if I could explain it decently, but I will say that it's not too hard, with regular exposure, to get a passive knowledge of the Î¼Î¹-verbs so that you'll be able to recognize what the forms are. But anyway:
1. The basic division with Greek verbs is between the thematic conjugation and the athematic conjugation, and roughly speaking, in the former endings are added with an Î¿/Îµ depending on the ending, and in the latter, endings are added directly to the stem. So to try and summarize:
The thematic conjugations are the present in -Ï‰ and the aorist in -Î¿Î½. Here you add -Î¿Î½Ï„- to get the participle, e.g. Î»ÏÏ‰ > Î»ÏÏ‰Î½ and á¼”Î»Î¹Ï€Î¿Î½ > Î»Î¹Ï€ÏŽÎ½.
Aorist verbs in -Î± are, I guess, technically athematic, but they're different from the rest, so you can treat them separately and just remember that the participle has -Î±Î½Ï„-, e.g. á¼”Î»Ï…ÏƒÎ± > Î»ÏÏƒÎ±Ï‚.
Those are the simplest cases, and fortunately the most numerous. Everything else is athematic (including the -ÎºÎ± aorists of Î¼Î¹-verbs), and to get the participle you need to add -Î½Ï„- directly to the stem. The problem with finding the stem is that it usually appears in a lengthened form in the principal part, so you have:
Î´Î¯Î´Ï‰Î¼Î¹ - stem Î´Î¹Î´Î¿-
á¼”Î´Ï‰ÎºÎ± - stem Î´Î¿-
á¼”Î³Î½Ï‰Î½ - stem Î³Î½Î¿-
Î´ÎµÎ¯ÎºÎ½Ï…Î¼Î¹ - stem Î´ÎµÎ¹ÎºÎ½Ï…-
Ï„Î¯Î¸Î·Î¼Î¹ - stem Ï„Î¹Î¸Îµ-
á¼µÏƒÏ„Î·Î¼Î¹ - stem á¼±ÏƒÏ„Î±-
á¼Î»ÏÎ¸Î·Î½ - stem Î»Ï…Î¸Îµ-
The problem here is that both -Î±- and -Îµ- are lengthened to -Î·- so you need to learn how to distinguish them. But basically -Î·- represents -Îµ- in Ï„Î¯Î¸Î·Î¼Î¹, á¼µÎ·Î¼Î¹, and the aorist passive, and -Î±- in most other places.
Once you know the stem, you just add -Î½Ï„- and you get the participle, so for those verbs above, you have Î´Î¹Î´Î¿ÏÏ‚, Î´Î¿ÏÏ‚, Î³Î½Î¿ÏÏ‚, Î´ÎµÎ¹ÎºÎ½ÏÏ‚, Ï„Î¹Î¸ÎµÎ¯Ï‚, á¼±ÏƒÏ„Î¬Ï‚, Î»Ï…Î¸ÎµÎ¯Ï‚.
2. In theory, you would go by the vowel the stem ends in. But the idea is that in certain forms the stem-ending vowel is lengthened, e.g. in the present, in all the singular forms. But there are all sorts of irregularities, even in what Pharr calls "regular" Î¼Î¹-verbs, so you almost have to learn each verb separately (verbs in -Î½Ï…Î¼Î¹ are all alike though), but there are generalizations you can make.
3. I think both are possible but some quick searching suggests that the nu movable is much more common.
4. Well, there are 11 forms in Attic Greek when you add the future passive. I don't know if that's how he gets 11 though.
5. Not much of an answer, but if they don't have all the forms derivable from a principal part, then they are defective in some sense. But if they don't have a principal part listed at all, then they don't have any of those forms -- if it had one of the forms but not the form that would usually be the principal part, they'd use a substitute principal part (if that makes sense). Like how some verbs have active forms in the present but only middle forms in the future, then the future principal part will be the 1st person singular middle.