Is this Itinerary too packed? What would you adjust?

Hey everyone! I'm planning a 2 month solo trip from late March to late May mostly through Asia with stops in Istanbul and Vienna before, and wanted to get a sanity check on the amount of time I'm spending in each place. I'd love to make it longer but that's the max I can get off from work :(

This will be my first solo trip, though a friend or two might join me for a leg.

Itinerary:

Here's my current set of flights and countries. The order in which I go (to most countries) is fixed because most of the ticket is booked on an Around the World ANA ticket, but I could alter the amount of time I spend in each city.

Out of all the countries on this list, I've only been to Japan (and really enjoyed it). I'm a relatively fit male in my mid 20s, working a corporate job in a big city in the USA, and pretty extroverted. I do enjoy a bit of luxury here and there so I was planning on splitting my trip between private rooms in hostels and switch to Hyatt hotels when I want to relax. I have heard Jakarta isn't the best, but only heading there to stay a night at the Park Hyatt. When I stay in hotels, I'll try to do walking tours and other activities to meet fellow travelers.

I really love food and trying new food, both high end Michelin type places and local street food. That's the primary reason I decided to do 3 days in Singapore bc I heard there isn't a ton to see but a lot of good food to try. Also like cities and walking around in general. I was also raised Hindu so I'm interested in exploring temples in Bali, and would potentially like to add 2-3 days in Siem Reap (to see Angkor Wat) into the trip in between Thailand and Vietnam. Do you think I should just take time out of Bali/Thailand for this or some other country?

Last, I think I'm going to get dive certified before the trip and try to do some dives in Bali and Thailand so recommendations for that would also be great. Messed up timing wise putting myself in Thailand in April, but hopefully I'll be able to deal with the heat. Plan to do Ha Giang loop in Vietnam and understand that I won't have time for much else there with the current set up.

Budget for the 2 month trip would be around $20k USD and ~300-400k Hyatt points (flights have been covered for about $2k of the budget). Definitely interested in splurging on activities and food if they're worth it. Probably book half the nights on Hyatt points.

Will probably repost here once I've gotten a more detailed itinerary with what I'm doing in each country day by day! Don't want to overplan as I might get real tired having never done a solo trip or a trip this long.

I'm curious of a couple things:

1. Which cities would you recommend staying in hostels vs just spring for the Hyatt? Mostly would be interested in hostels for the social aspect because in all other respects I prefer having a nice place, but love to meet people
2. Where would you add time or take time away? How would you squeeze Siem Reap in and for how long?
3. Is the itinerary in general sensible?
4. Recommendations for any / all of the countries on my list!
   1. Food, activities, places to stay, things to do. Anything that I should book in advance is also super helpful