10 days trip to Kansai region 3-12 May 2017

We are a family of 4 adults planning our 1st holiday to Japan and below is our itinerary:-
Day 1: morning arrival at Kansai Intl Airport. Transfer to Osaka and then Kyoto.
Day 2 - 4: Kyoto (4 nights at Kyoto)
Day 5: Kyoto to Uji and Nara (overnight at Nara)
Day 6: Nara to Mt Koya (overnight at Mt Koya)
Day 7: Mt Koya to Osaka and Arima Onsen (overnight at Arima)
Day 8: Arima Onsen to Himeji to Osaka
Day 9 - 10: Osaka (2 nights at Osaka)
Is this itinerary doable? Logistically speaking, would it be better to stay an extra night at Kyoto and to do a day trip to Nara and travel from Kyoto to Mt Koya via Osaka instead? Any input and suggestion would be much appreciate.
Thank you and regards.

May 3 is considered here as a peak of Golden Week the same as May 6-7 which is the weekend after holiday thus part of Golden Week.

http://www.japan-guide.com/e/e4904.html - Use the drop-down menu to check how to get to Koyasan from each location. Check Hyperdia/Jorudan/Google for your train or bus travels.

You may do Koyasan on the first or last part of your travel but I would like to think that your itinerary is final given the accommodation availability there and on your other locations.

Regarding the transportation from Nara to Koyasan, you may refer to the website below:
http://www.japan-guide.com/e/e4904.html?aFROM=2165_4900

Thank you for your reply. We only realised about the Golden Week in Japan after we have booked our flights.
So far, we have only booked our accommodation at Kyoto and will book the rest once we have finalised our itinerary.
Do we have sufficient time to enjoy the beauty, food and culture of each locations with our proposed itinerary?

Is this itinerary doable?

I think your itinerary is nice.

Logistically speaking, would it be better to stay an extra night at Kyoto and to do a day trip to Nara and travel from Kyoto to Mt Koya via Osaka instead?

Kyoto-Nara-Koyasan is very natural. If you day-trip to Nara and then to Koyasan from Kyoto, it should be a waste of time. If you have large luggage, Uji along the way to Nara may be problematic. You may better do Uji with some southern Kyoto places such as Fushimi Inari and Daigoji while you are staying in Kyoto.

Any input and suggestion would be much appreciate.

As for Nara and Koyasan, one night should be fine. However if you want to enjoy Onsen experience, you might better stay in a ryokan for two nights.

I am a Japanese and the Japanese way to enjoy Onsen is as follows.

Arrive 2-3 o'clock, check in and then go to the in-house onsen. After onsen, stroll town wearing Yukata. Go back to the ryokan and take a bath before dinner. Have dinner. Normally, it should be 6:00 to 8:00. You may want to walk around the town. Take onsen before sleep. Sleep in your room.

Get up early and take onsen before breakfast. After breakfast, take onsen again.

Honestly, Onsen accommodation is not cheap, so we try to enjoy as much as possible :). If you stay two nights, you can enjoy onsen in a more relaxed way. You can enter your room anytime in your second day.

Will you leave in the morning from KIX in your last day? If your leave in the evening, you can enjoy some of Osaka in your last day. Of course, it depends on your flight and your preferences.

Have you already seen the time you will spend on your travel from Nara to Koyasan and Koyasan to Arima Onsen?

Your itinerary is doable. You said you may opt to stay in Kyoto for your Nara tour, then do that. When you travel to Himeji from Kyoto, stay in the night at Namba/Shin-Imamiya/Tennoji in Osaka so you will have an easy access to Koyasan which you also prefer. From Koyasan, then arrive in Arima Onsen whatever time pleases you. At least onsen is your relaxation place before your fly home.

Another option. Depending on your time fly home, there is a bus from Koyasan leaving at 13:30 for KIX, if you put Koyasan on the later part of your Japan tour.