Hey, I'm not quite sure how to study for the usefulness and reliability questions in section 1 other than doing past papers?
Past papers is probably the best way to go now (especially if you can get them checked over!)
However something that might help would be to create a sort of "short cut sheet" for the perspective and reliability stuff. There are lots of ways to assess the reliability of a source (you should probably aim for 2-3 tests within your response for each source), some of which present themselves very easily depending upon what type of source they are, and can pretty much be used whenever you encounter this source type.
For example, If you are given an extract of a historians work, these tests for reliability will almost always be valid:
The source is HIGHLY (remember these buzzwords) reliable because it is:- The product of extensive research
- peer reviewed
- neutral/academic perspective (I know, if you do history extension that this is painful to write, but for modern its okay)
However the limitation of the source is that it is:- Incomplete by nature as an extract
Another example: A diary entry of someone at the time.
The source is HIGHLY reliable because it:- was created within close proximity to the time by someone who was (potentially if indicated by the sources) involved within the events discussed.
- was not written to be published ie. why would someone lie to themselves? (again this has issues, but they're not expecting you to be amazing historiographers in modern)
etc. etc.
See? Of course it would be perfectly fine to discuss other stuff, particularly if within the extract something else really jumped out to you that impacts upon reliability, but if you have these little cheat sheets, where you know that pretty much whatever source they throw you you will have a response will make you feel a lot more confident going into an exam. Just think of all the different types of sources they can give you, and try to create these short little note tables on each of them.
You can also do this with perspective.
For example, if the source is a diary entry or a letter, we can say that it presents a "deeply personal perspective".
Historian extract: "neutral, academic perspective"
Poster: "propaganda, thus presents and ideologically/politically motivated perspective"
If the source was written by someone/something that occupies a high-ranking position, eg. Lloyd George, mention that! Even though the "British perspective" doesn't really exist because everyone experience of the War was different, if it was from a high-ranking individual, you can say that they are presenting the "externally recognised perspective of the British" in that that was what other nations perceived to be the British perspective (If that makes sense. I'm still looking for a better phrase than "externally recognised perspective" if anyone has any ideas haha)
etc. etc.

So yeah, if you're getting bored just going over your notes and doing past papers, this would probably be a pretty good way to study instead, and will definitely help you feel more confident going into the exam, because pretty much no matter what type of source is given and no matter how complicated the contents of it may be, you'll still have something to write about.
Hope this helps and good luck! It'll all be over soon haha
*omg just realised how much I wrote sorry haha, a lot of this is probably just word vomit, a lot of me repeating myself, and stuff you probably know already, but hopefully somewhere along the way is something useful
