Complete noob traveler seeking advice

Hello!

I'm planning a trip to Japan for around 30 days at the end of March next year. I'm a bit of a newbie on traveling in general, and it will also be my first time ever doing a trip that long and also my first time ever solo traveling, so I have some doubts about packing that I hope you guys can help me with.

My idea is to travel "light", carrying a big backpack that I will leave at hostels and then have a smaller backpack for the daily roaming around, but I'd prefere not to bring a suitcase.

I've looked into the subreddit and into the Onebag comparison list but still I'm a bit lost on some aspects:

1. Which bag size would you recommend for that kind of trip? I've seen recommendations up to 40L, but I've also seen people do 2-3 weeks with a 20-25L bags. Right now I have a 20L SZLX backpack I bought from Amazon, fitting the max size for underseat bags on European flights (I think international flights allow bigger underseat bags?) but I'm worried it might be too small.

2. I'm a bit worried about the weight aswell, since I've seen that in long flights airlines weigh your backpack. How do you guys handle this?

• If my backpack weighs too much do I have to check it?
• Can you carry it onboard but paying extra for the overweight?
• Is it safer/better to just check it from the start?

(Sorry if this is not the place to ask this, I've never had to check a bag before so I don't wanna get surprised at the airport)

3. This is what I was thinking about bringing with me. Is it too much? Not enough? Am I missing something?

Essentials

• Phone
• Passport
• Wallet

Clothing

• 5-6 T-Shirts
• 1 Pair of long pants
• 1 Pair of shorts
• 1 Jacket
• 1 Raincoat
• 7-8 Underwear & socks
• 1-2 Long-sleeve shirts
• 1 Extra pair of shoes
• 1 Pair of flip flops for the shower
• 1 Small fast-dry towel

Electronics

• Chargers
• PowerBank
• Earbuds
• eReader
• Camera? (I don't own one currently, so I'm debating if I should get one or just use my phone)

Personal care

• Shampoo
• Dehodorant
• Tooth brush
• Tooth paste
• Shaving machine

Thank you so much to everyone in advance. Sorry if something isn't clear or hard to understand, English is not my main language so some things might be a bit confusing.