What's the reason about cheshvon? Anything to do with the mabbul?
P.S. I was referring to the end of any month (with exclusion of adar and elul iinm)
I have no idea what it is about Cheshvon, IINM Teves was also not a very popular month.
But as I said, and concurred by @Freddie, in this generation almost all restrictions are off.
As for the Kinnus being timed around Shabbos Mevorchim Kislev, while someone might ask the organizers how it got started, my guess is that it was simply because it was close to Rosh Chodesh Kislev - a major Yom Tov for דור השביעי and also close to פרשת חיי שרה which describes the first שליחות, even though it has been brought upthread that it's about Shabbos Mevorchim Kislev and not about פרשת חיי שרה.