I agree it’s busy, but I don’t really find it stressful….we have our youngest’s birthday mid-October, similar to you, but have always just done parties at home on our farm (this year we had some of his friends over, swam in the pool and they stuck a tent up and camped out in the garden). We also don’t go mad for gifts, he had some rugby training stuff, a few books, Pokemon cards and various other little bits and bobs.
For Halloween I usually throw together a costume for each boy in the few days before from things we’ve had in previous years (or buy one from a charity shop). They are old enough now that they don’t really go to Halloween parties (11 & 14), but they do go out trick or treating in the village with friends. We don’t decorate the house as we’re on a farm and no-one can see our house from the road. The kids carve pumpkins usually the day before Halloween and we just light them in the evenings by the woodburner, until they start going mouldy!
There are a lot of friends birthdays in Oct & Nov, rugby season is in full swing, plus cross country races, swim galas and winter triathlon. We just limit it to one fixture / comp per child per weekend and make sure on the weekends they don’t have anything on, that they get some down time just relaxing at home etc as school is also very busy with sports stuff too. It feels quite good to say no to things sometimes too - the kids want to do everything, but I prefer them not to be overstretched.
I’ve just booked our annual ski holiday over Christmas which is something to look forward to but also means I know have to organise house sitters or kennels for the dog & a groom to come in for the horses, plus cover for the farm animals, for that week. To be honest though, I think spring is our busiest time and so autumn doesn’t feel too bad in comparison - I don’t like the darker evenings and colder weather though which is why I’m a bit anti-autumn.