Yes you submit a solo to the HD.
Long enough to catch the god's attention.
CS should be reasonably complete, though if your history is dependent on the gnosis it's probably forgivable for that to not be fleshed out yet.
The founder judging your gnosis request will most likely tell you what's wrong with your story, and you should be allowed to re-do it (if this doesn't happen, try specifically requesting feedback, because feedback takes effort and if you're just going to give up instead then it's not worth giving
).
I think it's mostly about the premise being suitable and also you portraying the god correctly. The test of actually using the gnosis will come in regular roleplay, and will determine how likely you are to get a second mark