1. The gemara (Sotah 36) writes that Pharoah's advisors objected to his appointing this unknown slave named Yosef to a position of power. Pharoah answered that he saw royalty in Yosef. The advisors responded that if Yosef was indeed royalty, then he should be able to speak in 70 languages just like Pharoah, and he should be put to the test. The gemara says that Gavriel came and tried to help Yosef cram (better than using rosetta stone), but he wasn't getting it. Gavriel then added the letter hey to Yosef's name -- "Eidus b'yehosef samo [darshened as shemo=his name] b'tzeiso al Eretz Mitzrayim -- and he was then able to learn the 70 languages.
If Pharoah was able to master 70 languages, how was it that Yosef, "ish chacham v'navon," not to mention a tzadik, was incapable to doing so? Was it the time pressure, or the pressure of doing it for the test put forth by the advisors?
Maharal (Gevuros Hashem ch 28) explains that Moshe's speech impediment was not a flaw or a defect. Speech has to come from the chomer, the body, as well as the nefesh. Because Moshe was so spiritual, he was disconnected from the world, and was unable to connect to his guf to properly express himself through that medium.
R' Zev Hoberman z"l similarly explains that when the world was first created and was in a pristine, spiritual state, the only language that existed was lashon kodesh. The 70 languages came into being as a result of the sin of dor ha'palagah. Yosef's neshoma was still on that pristine, high level of spirituality, and therefore, it connected only with lashom kodesh. Its inability to express itself in other ways was a feature, not a bug.
2. The Midrash darshens Yosef's instructions "tvo'ach tevach v'hachein" as an allusion to Shabbos, which requires hachana, preparation. Since Yosef is described as a shomer Shabbos, therefore, his descendent was zocheh to offer korbanos at the dedication of the mishkan on Shabbos. The prince of Ephraim is the nasi who brought his korban and gift on the 7th day of the chanukas hamishkan.
Even though Yosef gave those instructions, the other shevatim as well as the Avos also observed Shabbos. Why is the reward given only to Yosef?
The Midrash in last week's parsha writes that had Reuvain known that the Torah would write that he saved Yosef, he would have grabbed him from the pit, hoisted him on his shoulders, and brought him home. Does that mean that Reuvain would have done more if he would have known about the great publicity he was going to get? Of course not. The Sefas Emes explains that what Chazal are telling us is not to minimize the significance of our own actions. A person who does a good deed may think to himself/herself, "What does it matter how I do it, what I do, how much I do? At the end of the day, what difference is my small effort going to make?" That mindset leads to discouragement, for doing less than the optimal, for giving less than 110% The truth is that every action we do makes as world of difference for ourselves and for our offspring, who learn from what we do. Every action is Torah. Had Reuvain realized that his efforts were Torah, and were not an insignificant fruitless attempt, he would have put more into it. (A few years ago I wrote up a different pshat here.)
I think that is what Chazal are getting at in this Midrash regarding Yosef as well. Of course the Avos and shevatim observed Shabbos, but there observance, for whatever reason, is not recorded explicitly, and therefore is not torah in the same was as Yosef's shmiras shabbos. What is recorded in the text is a limud for all doros for all eternity. Only Yosef merited that. (Why that is true, I'm not sure -- you can say whatever sevara you like.)
The effect it had on Ephraim being able to offer his gift on Shabbos is not a reward -- it's a consequence (all rewards in Torah are really consequence, but that's a discussion for some other time.) By definition, since Yosef's shemiras Shabbos was torah, it had an effect generations later, because that's what Torah is -- it is eternity. (See Bad Kodesh by R' Povarski who has a different approach.)
3. Put yourself in Yosef's shoes -- what would pop into your mind as soon as you see your brothers? Wouldn't you think to yourself, "These are the guys who sold me down the river!" But look at what the pasuk says, writes the Alter of Navardok: "Yayizkor Yosef es ha'chalomos asher chalam lahem" (42:8) Yosef thinks only of the dreams he once had, not what his brothers had done to him, and certainly not of revenge.