1. Well, did it state that itachi used tsukyomi to kill his clansmen?well by the context I'd say hes talking about showing his MS in the first scan and Tsukuyomi in the second.
Lets look at what happens on the first scan, it starts with Itachi saying "you are not related to the uchida. we are the true masters of the sharingan still.. your body is suitable for the eye.. but it does not contain any of our blood" then he continues "Do you know why the uchida clan is the most powerful and feared clan of all? I will show you the true powers of the Bloodline of the Sharingan masters!" this makes me think he's talking about his MS which is needed to preform Tsukyomi in the first place. And as Kakashi nor anyone else ever mentioned MS and it leads to itcahis most powerful jutsu(Tsukyomi included)that would lead me to believe that hes speaking about his MS which he assumes kakashi not being from the uchiha doesnt know about, and as no non-uchiha besides kakashi has even been shown or mentioned being able to use MS (except danzo who possessed uchiha DNA from all those eyes implanted in his arm as well as having senju inplanted in his body as well as not existing in the naruto universe until shippuden chapter 284 page 17 so im guessing he wasnt even thought of until way after those scans from the original naruto)/ Plus the fact that in the next scan shows Itachi saying "that is true only another sharingan user could challenge me... some resistance could be made to thise mage-sharingan. However this sharingan has a special eye jutsu. My illsusion jutsu "Tsukiyomi" cannot be beaten! Only a sharingan user with the same blood as me can defeat me.." And as kakashi [since danzo wasnt created yet] was the only non-uchiha to ever be shown or even mentioned possesing a sharingan or shown to be hit with Tsukyomi, and makes me think he is also including other uchiha in not being ale to break it since everyone else with it a sharingan is an uchiha. Plus i assume he used it on the uchiha durring his massacre of them and since not a single person has even been shown or stated to counter it except sauske(his 100% blood brother) that's what makes me think it has to be a sibling. Do you get what im saying?
when was it stated he would die if he did it by himself? All I remember them saying was it takes longer with less peopleYou must be registered for see images
It looked like shurikenjustu during the flashback.
Also Danzo transplanted Shuishi's eyes when he activated MS (just like itachi's crow), mokuton was a means of controlling the eyes.
Danzo doesn't have uchiha DNA, but he has the sharingan.
Like in order for you to have the sages power you need to have senju blood and uchiha blood with the ocular powers.
That's why Obito stated he had the incomplete form of inzangi, otherwise he would match Obito in terms of power.
During the battle against Sasuke, Obito explains it better.
2. I didn't know how to explain nagato's use for Gedo damaging him, instead of Obito.
So I thought that can be a valid excuse.
It took a while for Obito to use it without the rinnegan...
At least you notice...
Madara did say you can't use the statue properly without being uchiha and senju with rinnegan eyes, but since he is both uchiha and senju, eventually he will be able to use Gedo mazou.