Why didn't Yitzhak marry Bakol and Why is Bakol Mentioned Here?

The gemara Bava Batra 141a and Bereishit Rabba 59:10 bring down an argument regarding whether Hashem blessing Avraham "Bakol" means that he had a daughter or that he didn't have a daughter.

Tosafot in Bava Batra (ד"ה בת היתה לו) ask why Yitzhak didn't marry Bakol according to the opinion that he had a daughter since a Ben No'ah is permitted to marry a sister.  He answers either that she was a Ketana (a minor) at the time or that she was the daughter of Hagar, which was undesirable.

The Maharam on that Tosafot is implicitly bothered by Tosafot's first answer - Rivka herself was a minor as she was 3 when Eliezer went to find her, and Yitzhak ended up marrying her, so why the double-standard?  He answers that he must follow the alternate opinion that says that she was 14 when she got married, and he directs you to Tosafot in Yevamot 61b (ד"ה וכן הוא אומר) who explain this alternate opinion.

The נזר הקדש (left column, 17 lines from the bottom) asks why this verse (of וה' ברך את אברהם בכל) is brought here right before sending Eliezer out to find Yitzhak a wife.  According to the opinion that "Bakol" means that he didn't have a daughter, we can easily answer that it was brought here to teach that Avraham had no daughter for Yitzhak to marry and he therefore needed to send Eliezer out to find him a wife.  However, according to the opinion that "Bakol" means that he did have a daughter, why was this brought down here specifically?

He answers this nicely.  The Midrash later says (by the same author who holds he had a daughter himself - ר' יודן) that Avraham getting his son married first and then marrying himself teaches us Derech Eretz - that if a man has older children, he should marry them off first, and then get married himself.  However, this idea only applies if the man had already fulfilled the Mitzvah of Peru Urvu, but if he hadn't yet, he should get himself married first.  Only now that Avraham had had a daughter to add to his 2 sons could we say that he fulfilled the Mitzvah of Peru Urvu.  So, only now should he be busy in getting his son Yitzhak married off.  This is why this verse is mentioned here.

(So now why according to the opinion that holds he didn't have a daughter didn't Avraham get married first since he didn't fulfill the Mitzvah of Peru Urvu yet?  Perhaps, since ר' יודן is the author, and he holds that Avraham had a daughter, we could possibly say that ר' נחמיה (who argues and says that he didn't have a daughter) doesn't hold of the concept at all since according to him, it makes no difference who gets married first, and there's no Derech Eretz involved at all.)