2, I don't like stories with a lot of focus on other characters and from what was said the ban is the MC's brother or friend for so long that I don't even remember so it will be someone else with knowledge of the plot, stories with more than one reincarnated are rarely good in fanfiction.
2 and what do you mean Rias and Yasaka and Gabriel are not in the issei harem 8 times nor kissed his harem totally useless guy that the author created this mc f please rias in the harem
no crossover wouldn't be a need to add them in, this is a new ban just make it memories of a past life he recalled in a dream and to keep memories of his old friends alive