Irish Relative Clause Patterns
So there seem to be a number of relative clause patterns in Irish that I need to practice:

Direct Relatives:

1a. Bhuail mé leis an bhfear a cheannaigh an leabhar.
I met the man who bought the book.

1b. Chonaic mé an leabhar a cheannaigh an fear.
I saw the book that the man bought.

1c. Bhuail mé leis an bhean an bhean lena dúirt sé é. (lena clause)
I met the woman with whom he said it.

Indirect Relatives:

2a. Bhuail mé an bhfear ar cheannaigh siad an leabhar dó. (inflective prep. dó)
I met the man for whom they bought the book.

2b. Bhuail mé leis an bhfear ar cheannaigh a chara an leabhar. ("whose X" clause)
I met the man whose friend bought the book.

2c. Bhuail mé leis an bhfear ar cheannaigh a chara an leabhar dó. ("whose X" clause + inflected prep. dó)
I met the man whose friend bought the book for him.

3. Bhuail mé leis an bhfear a molann na mic léinn é. (resumptive direct object pronoun é)
I met the man whom students praise.* 1c. "... leis an mbean..." if I am sticking to the same dialect throughout all of this, right?

This seems like another one. I got this from Wiktionary's entry for "lena". Shouldn't that be "a ndúirt" though? Hmmmm.

Bhuail mé leis an mbean a dúirt sé léi é.
I met the woman that he told it to.

Question

Irish Relative Clause Patterns
So there seem to be a number of relative clause patterns in Irish that I need to practice:

Direct Relatives:

1a. Bhuail mé leis an bhfear a cheannaigh an leabhar. 
I met the man who bought the book.

1b. Chonaic mé an leabhar a cheannaigh an fear.
I saw the book that the man bought.

1c. Bhuail mé leis an bhean an bhean lena dúirt sé é. (lena clause)
I met the woman with whom he said it.

Indirect Relatives:

2a. Bhuail mé an bhfear ar cheannaigh siad an leabhar dó. (inflective prep. dó)
I met the man for whom they bought the book.

2b. Bhuail mé leis an bhfear ar cheannaigh a chara an leabhar. ("whose X" clause)
I met the man whose friend bought the book.

2c. Bhuail mé leis an bhfear ar cheannaigh a chara an leabhar dó. ("whose X" clause + inflected prep. dó)
I met the man whose friend bought the book for him.

3. Bhuail mé leis an bhfear a molann na mic léinn é. (resumptive direct object pronoun é)
I met the man whom students praise.* 1c. "... leis an mbean..." if I am sticking to the same dialect throughout all of this, right?

This seems like another one. I got this from Wiktionary's entry for "lena". Shouldn't that be "a ndúirt" though? Hmmmm.

Bhuail mé leis an mbean a dúirt sé léi é.
I met the woman that he told it to.

Answer

In 1 you're mixing up dialects (and their respective grammars): leis an bhfear, leis an bhean. You should either have "leis an bhfear" and "leis an mbean" OR "leis an fhear" and "leis an bhean".
In 1c you should have "lena ndúirt sé é", since it is an indirect relative. You could alternatively say "a ndúirt sé léi é". 
Also you English translation for 1c sounds a bit strange. I know it's a literal translation, but "to say something with someone" it doesn't really make much sense in English: better to use "to" instead of "with".

2a: Bhuail mé LEIS an bhfear... (!)

3. THE students

Reading to the end, I see you picked up on most of those by yourself.

Bulaí fir!