Omuro 88

I'll be in Japan this year in time for the Omuro 88 at Ninna-Ji to be manned, which happens about six times a year as I understand.

Has anyone been to one of those events and can advise how packed full of people I can expect it to be?

Thanks!

No packed.
http://www.ninnaji.jp/hallowed_ground/
Walk 3 km in about 2 hours.

Just go to the reception on the day btw 9:00 to 12:00, pay entry fee 300Y and recieve a stamp book.
The decision on whether to cancel the event will be announced at 7:30 in the morning.

There is no rule of clothing, shoes and more special manners.
But there are some hard slopes, would be better rucksacks for both hands free.
and in the forest, it may be better to avoid black clothes that bees(hornets) hate color.
Anyway, just follow other participants and ask if wondering.
You can break(rest), talk and even eat and drink(No liquor) in the middle.
http://dot117.minibird.jp/wp/?p=917
http://ropuchan.cocolog-nifty.com/blog/2008/09/post-31ec.html
http://rinppa.hatenablog.com/entry/2016/09/04/180743
Some people preparing offerings(1Y coin or more) for 88 spots apart from entry fee,
but it is not "must", some 5Y coins enough. (5Y coin has "make good relations")
https://scarlet-seals.clover-and-rainbow.com/wp-content/uploads/2015/10/N88-1.jpg
https://en.wikipedia.org/wiki/5_yen_coin
Vinegar and salt can only remove dirt like this, though,
https://youtu.be/mQSsyBRzM88
but you can get new coins is not so hard, ask to casher staff of shops.
If going to supermarket(grocery store), "service(infomation) counter" will be better than cashier.
http://livedoor.blogimg.jp/bbookk20112012-saitama/imgs/b/b/bbf91c79.jp...

Thank you very, very much for your detailed answer!