Interrogative/Counters with か、も、でも, but also with particles

Question

I know that by attaching か、も、でも to the end of an interrogative word can form a new meaning, but if particles are also used, where should the position of each thing be?

Example:

Which day?
いつの日？

Some day...
いつの日か…

But, "Until someday" should be which of the following?
いつの日までか　OR　いつの日かまで?

Also, I have the impression that counters work differently than these interrogative words. For counters, it's always 「counter」+「か、も、でも」+の+「noun」， unless counter is used after the noun. For example:

With some students:
何人かの学生と　✅
何人の学生かと　❌
何人の学生とか　❌

Buy however many cars:
何台でもの車を買う　✅
何台の車でもを買う　❌
車を何台でも買う　✅

On some websites:
いくつかのウエブサイトで ✅
いくつのウエブサイトかで ❌
いくつのウエブサイトでか ❌

Am I correct about these? Or the ones that I think are wrong are in fact correct?

Answer 1

"Until someday" usually has to be いつか来る日まで or いつか来るその日まで. いつかの日まで is also used, but this is uncommon in my opinion. Alternatively, if you know what will happen on that day, you can use the corresponding verb and say something like this:

• さようなら、いつかまた会う日まで。
• この悪魔がいつか復活する日まで、私はこの門を守り続けます。

何台でもの車を買う is a wrong sentence. Otherwise your chart is okay.

Buy however many cars:

何台でもの車を買う　❌ ← !
何台の車でもを買う　❌
車を何台でも買う　✅
何台でも車を買う　✅