Seems like a reasonable route. But i can't say what is a bad route in Iran, the people are nice everywhere you are.
Yes, i agree, the Tehran isn't the nicest place. But indeed, if you look from the feeling of Asian city aspect and want to experience it, go for it.
I remember despite the traffic that was so dense and slow that the cars almost scratched each other, they always leaved a huge space for me - probably they understood instantly that i'm foreigner with a big GS enduro with ally panniers etc (over 250cc bikes are banned for iranian citizens).
But indeed, it wasn't nice while it's some over +40C temperatures out there and you move few metres per second in that traffic!!! I was there last year at the same time as you are now. I think only idiots go there this time of summer
, but we adapted with the heat in Iran about 1 week we was there and it was OK in the end, could ride around with thick black riding jacket that sucked the sun.
Consider trans- Dast-e-Kavir road, that was one of the highlights for me. From flat bloody hot desert to steep high refreshing mountain chain in the middle of the desert, fantastic nature.
Yazd and Esfahan were the absolute favorite cities i visited.
Safe travels, Margus