i didn't ask you to reply but thanks for wasting my 10 minutes to read it. minato has no experience in fighting the uchihas like itachi, he has not seen the susanoo and he doesn't know how to counter tsukyomi so he doesn't know thier abilities. and if kakashi and even sakura was able to figure out the ability of warping objects into other dimension then obviously itachi would have figured it out too and then thought of some way to counter it.
If minato didnt know anything about Uchihas then how did he conclude(although it was wrong) that masked man could be madara,this definitely means he knew about Uchiha and their abilities.....
Even if itachi figures out how dimension techniques work,how is he supposed to reach the other dimension to attack Minato
If Itachi uses Yasaka Magatama or amaterasu,minato can teleport them to other dimension and throw back at him as they r samller than bijuudama(like minato transported kyuubis bijuudama and it reqd. A lot of chakra)
Minato is extremely fast at sealing techniques as seen in his fight with B,totsuka blade and elemental techniques will hardly damage him
Even if amaterasu hits minato,he can send it to other dimension(like tobi did)
He can use gamabunta to crush susanoo
Yata mirror can provide defense upfront and hemce minato can move behind using raijin and hit from behind
And as for genjutsu,this is an assumption but most probably correct,seeing as to how he is a kage level jounin,he must hv trained himself in some way to defeat genjutsu,he is a hokage,after all......
Also,he can always use reaper death seal which is pretty fast(3rd wasnt fast as he was old and so reaper death seal wasnt fast)....source-Wiki