だとする、うえで、よう in this sentence

Question

総会のあと、公明党大阪府本部の佐藤代表は、記者団に対し、都構想そのものへの賛否は白紙だとしたうえで、「法定協議会が再開されれば、いい協定書を作れるよう前向きに協力していくというのがわれわれのスタンスだ」と述べました。 (source)

Here is my attempted translation:

After the general meeting, the representative of the New Komeito Party Osaka Prefecture Administration, Mr. Sato, told to reporters, when assuming the opinions on both sides towards the Metropolis Plan have not been made, "If the statutory committee is reopened, our stance is that we will positively cooperate together to make a good agreement".

What does だとした mean? From what I know, だとする could mean "assuming that, when used with a noun"

彼の死は事故だとする君の推定は間違っているようだ。
Your assumption that his death was an accident seems to be wrong.

病院は頭痛の原因を睡眠不足だとした。
The hospital assumed the cause of the headache to be a lack of sleep.

But I'm not sure if this interpretation is correct for that sentence.

Also, is うえで the same type of 上で like in this example?

これまた西欧文明を理解するうえで、忘れてはならないことでありましょう。 Again, let's not forget this when trying to understand Western European civilization.

I translated it as "when"

And lastly, what does the よう in いい協定書を作れるよう前向きに協力していく mean? I assumed it was ように but I never seen it without the に before. Like in this sentence:

風邪を引かないようにちゃんと寝てください。Get some sleep so you don't catch a cold.

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Here are my questions:

1. Is my interpretation of だとする correct?

2. Is my interpretation of うえで correct?

3. What does よう mean?

Answer 1

You understand everything correctly. There is no such thing as だとする. It's とする and だ is just there because there was a noun. If it was a verb or adjective you'd just use とする. And following this, obviously you can conjugate it.

Noun particles(?) like 為{ため}、様{よう}、余{あま}り, don't necessarily need に after them to function.