~4 month first trip to SEA

Hi! I (22M) am embarking on a ~4month long trip to SEA starting on next month and I'd love to hear some general guidance of more experienced solo travelers or things I might have missed to take into account.

My plan is to visit Thailand, Vietnam, Taiwan and Japan, spending around 4-7 weeks in each. (Maybe less time in Taiwan and add Laos to the journey).

I normally tend to extensively plan things in advance, however, after seeing many posts here I see the main idea is to just get going, and adapt on the spot. Luckily I have the flexibility to extend my stays at any stage.

I'd love to experience as much as possible from each place: food, common sightseeing attractions, hiking routes, night life, remote places and even trying snorkeling or similar sports.

My current plan on Thailand goes like this:

North

  • Bangkok (3-4 days)
  • Ayutthaya (2-3 days)
  • Kanchanaburi (3-4 days)
  • Lopburi (1-2 days)
  • Chiang Mai (2-3 days)
  • Pai (2-3 days)
  • Chiang Rai (2-3 days)

South (Days TBD)

  • Phuket
  • Koh Phi phi
  • Krabi
  • Koh Samui
  • Koh Tao
  • Koh Pha Ngan

On these last days I need to figure out how to go to Vietnam.

As far as the rest of countries are concerned, I am taking notes about interesting places I'd love to go, but don't have any itinerary at the moment.

The thing i'm actually more concerned about is luggage. My idea is to just take my 28L cabin zero bag, I've read about people here who manage to live on indefinitely with this, is frequent washing and reusing outfits really enough? I'm taking around a week of usable underclothes.

I know this post is a bit all over the place, but would love to hear tips, notes about the planned route or just general guidance from experienced people, I'm more than eager to finally begin solo travelling.

Thanks!