The use and placement of だけ


I just learned some stuff about the use of **だけ** and now I wonder, if I want
to say

`"Just me and a friend did this"` , could I use **だけ** to express this?

If so, how would I have to use it? And when would I have to refrain to using
`一人で`?

This also raises the question whether 一人で could modify a verbal expression
related to a subject which represents multiple persons?

> 1a) これは私と友達がするだけだった。 1b) 私と友達だけはこれをした。
>
> 2a) これは私が一人でした。 2b) これは私と友達が一人でした。

I assume that 1b) is pretty ungrammatical, but I wanted to ask about it
nevertheless because it is stated in my textbook that だけ can be attached to
nouns.

This is in different context though, like here: `休みは日曜日だけです。`

I might be digging too deep now, but I wonder whether だけ and 一人で are one of
these things which don't modify a specific sentence element, but rather the
whole sentence.

Unfortunately I don't know what these are called in English terminology; in my
German linguistics lessons they were called "partikel".

I could give an example here:

> " **Of course** I can do this."
>
> " **Eventually** the machine crashed."




To avoid confusion as to whether it's "you and friend(s)" or "you and one
other friend", you may want to phrase it this way:

> これは友達と二人 **だけ** でした。  
>  **Only** a friend and I did this.

Assuming the context of you showing that you worked on this directly, you're
implicitly stating that you're a part of this group because 友達と = 'with a
friend' or 'with friends', but also 二人だけで is explicit about two people, so if
there's you, there's only one other person which is your (one) friend. This
also probably sounds the most natural.

