old man -“According to many, the Yud Gimel Midos may be said without a minyan, providing they are read as if reading (leining) from the Torah.”
I never do because that’s not the reason I’m saying it -so even though technically it’s ok -whom are you fooling?
As far as Tachnum in Mincha -I’m pretty sure that it is a Minhag not to say. While I believe this Minhag started because sometimes Mincha was finished too late to say Tachnum -this has become the Minhag (Not saying) all the time – No matter when you actually finish!