思ったんだけど meaning + って vs は distinction

So the example sentence is:

思ったんだけど、Aさんって、凄くいい人だよね

I understand the meaning of the verb 思う and I understand that its te/ta forms are 思って・思った。What's confusing me is 思ったん as well as the use of だけど afterwards. I've been thinking it means "I've been thinking" or "I'm wondering" or something along those lines?

Secondly,

The distinction between Aさんって、凄くいい人だよね and Aさんは凄くいい人だよね is blurry to me. I've heard that って is both more colloquial and often used when the topic incurs some form of emotion (ie. 田中さんって先生だ would be an incorrect usage of って?)

That's not 思ってた but just 思った, i.e., it's past or perfect.

ん is so-called "explanatory の/ん".
Noun-related particles - Tae Kim's Japanese grammar guide

だけど is used to introduce the main clause, not an adversative conjunction.

～って states that the preceding noun/phrase is going to be treated as a topic in that sentence, as same as ～というのは. It's not always interchangeable with は. In fact, in the sentence Aさんは凄くいい人だよね, は can perform as the contrastive marker and therefore it could unnecessarily emphasize Aさん (e.g. connoting Aさんは凄くいい人だけど、Bさんはそうじゃない).

田中さんって先生だ seems to mean 田中さんという先生だ to me. Anyway, it's at least not the same meaning as 田中さんは先生だ, either.

So んだ is a replacement for の/のだ？What would be the closest translation of 思ったんだ and 思ったんだけど？After reading through that page, it would lead me to believe that 思ったんだ is "(the thing is) I was thinking/thought". I am not sure exactly how けど functions in this instance. It doesn't seem to make sense to me to write "but, A is...". Unless it's just softening 思ったんだ.

Would it be correct to say that it means: "I was kinda thinking (fairly soft)... A..."

の and ん are not always interchangeable, either, because of collocation, degree of colloquialness or level of politeness.

思う doesn't mean "to think" here. It's more close to "to realize". The speaker has just realized that Aさんって、凄くいい人だ.

けど is not an adversative conjunction, as I wrote in my pevious post. I.e., it doesn't mean "but", but shows that the following main clause is "what I've just realized".

Ahh, I think I understand now. Thanks for your help