I go to Takao San every year. Lately I go with my (Japanese) father-in-law (in his 70s) and my daughter (just turned 9).

For us, walking up and down is the main point of the visit (I like walking path #6 ). You can get a cable train that will take you a big chunk of the way up, but we’ve been using it less and less over the past few years.

A highlight for us is the public bath sento at Takao San Guchi Station. The facilities are excellent and there is a nice relaxing restaurant inside with good prices where you can chill out (chairs or tatami) after your bath. It’s a lovely way to end a hike.

Near Takao San Guchi Station is a small town with lots of restaurants. Before going up we generally choose somewhere for soba (buckwheat noodles). A speciality of the area is Tororo soba - grated yamaimo (a long thin tuber) is served with the buckwheat noodles, hot or cold. The yamaimo when grated has a snot like consistency. I’m very partial to it.

If you want to make a visit here into more of an event then you can combine a hike with a visit to Ukai Toriyama, perhaps the most beautiful restaurant in the Tokyo area. Lunch sets are around 5,000yen, food is delicious. Wonderful place, can’t rcommend it highly enough. But you should certainly make a reservation. The restaurant offers a complimentary shuttle service from the station.

You haven’t said what time of the year you want to visit. If end of December or early in the year - snow can descend within a very short time. We got into trouble one New Year’s Day where the weather was clement on the way up but we had to deal with inches of snow and treacherous ice on the way down. We still enjoyed the experience, but it was just me and my husband on that occasion.

I would advise not to visit the Monkey Park. My father-in-law took his granddaughter once, which meant I went too. It was even more depressing than I had expected it would be.
There are plenty of places for snacks once you near the summit, no need to pack too many supplies.