Participles and Relative Clauses

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Hello. I am doing a theoretical syntax project on Russian participles, and I have a few questions about whether certain forms are possible. I am aware that participles in general are not used in colloquial speech, and some of the forms I'm suggesting are indeed awkward beyond belief, but I am concerned more about whether something can ever be used, rather than whether it's stylistically ugly.

1. It seems that passive participles act almost identically to adjectives. Is the same true for active participles? In particular, is it possible to have short-form active participles as predicates? For example:

Она читающа книгу
Она была читающа книгу

Or are these forms bad, and instead I simply use the verb itself:

Она читает книгу.
Она читала книгу.

2. Active participles can modify full nouns:

Он видел человека, читающего книгу.

Can they modify pronouns?

Он видел меня, читающую (or читающего, if I were a man) книгу.
Он видел его, читающего книгу.
Он видел нас, читающих книгу.

3. In cases when there is a relative clause after a pronoun, I have seen constructions like the following:

Он видел того, кто читает книгу.

When the pronoun is not third-person, what person does the embedded verb take? In other words, which of the following is correct?

Он видел меня, кто читаю книгу
Он видел меня, кто читает книгу.

Thank you for your help. I imagine as I work further on this paper I will come up with more questions.